| Message ID | 20240912035945.667426-1-yonghong.song@linux.dev (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf-next,v2,1/2] bpf: Fix a sdiv overflow issue | expand |
On Wed, Sep 11, 2024 at 9:00 PM Yonghong Song <yonghong.song@linux.dev> wrote: > > Zac Ecob reported a problem where a bpf program may cause kernel crash due > to the following error: > Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI > > The failure is due to the below signed divide: > LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808. > LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808, > but it is impossible since for 64-bit system, the maximum positive > number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will > cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is > LLONG_MIN. > > Further investigation found all the following sdiv/smod cases may trigger > an exception when bpf program is running on x86_64 platform: > - LLONG_MIN/-1 for 64bit operation > - INT_MIN/-1 for 32bit operation > - LLONG_MIN%-1 for 64bit operation > - INT_MIN%-1 for 32bit operation > where -1 can be an immediate or in a register. > > On arm64, there are no exceptions: > - LLONG_MIN/-1 = LLONG_MIN > - INT_MIN/-1 = INT_MIN > - LLONG_MIN%-1 = 0 > - INT_MIN%-1 = 0 > where -1 can be an immediate or in a register. > > Insn patching is needed to handle the above cases and the patched codes > produced results aligned with above arm64 result. > > [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/ > > Reported-by: Zac Ecob <zacecob@protonmail.com> > Signed-off-by: Yonghong Song <yonghong.song@linux.dev> > --- > kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 80 insertions(+), 4 deletions(-) > > Changelogs: > v1 -> v2: > - Handle more crash cases like 32bit operation and modules. > - Add more tests to test new cases. > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index f35b80c16cda..ad7f51302c70 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -20499,13 +20499,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */ > insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code); > > - /* Make divide-by-zero exceptions impossible. */ > + /* Make sdiv/smod divide-by-minus-one exceptions impossible. */ > + if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) || > + insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) || > + insn->code == (BPF_ALU | BPF_MOD | BPF_K) || > + insn->code == (BPF_ALU | BPF_DIV | BPF_K)) && > + insn->off == 1 && insn->imm == -1) { > + bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > + bool isdiv = BPF_OP(insn->code) == BPF_DIV; > + struct bpf_insn *patchlet; > + struct bpf_insn chk_and_div[] = { > + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > + 0, 0, 0), > + }; > + struct bpf_insn chk_and_mod[] = { > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > + }; > + > + patchlet = isdiv ? chk_and_div : chk_and_mod; nit: "chk_and_" part in the name is misleading, it's more like "safe_div" and "safe_mod". Oh, and it's "sdiv" and "smod" specific, so probably not a bad idea to have that in the name as well. > + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : ARRAY_SIZE(chk_and_mod); > + > + new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > + if (!new_prog) > + return -ENOMEM; > + > + delta += cnt - 1; > + env->prog = prog = new_prog; > + insn = new_prog->insnsi + i + delta; > + goto next_insn; > + } > + > + /* Make divide-by-zero and divide-by-minus-one exceptions impossible. */ > if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) || > insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) || > insn->code == (BPF_ALU | BPF_MOD | BPF_X) || > insn->code == (BPF_ALU | BPF_DIV | BPF_X)) { > bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > bool isdiv = BPF_OP(insn->code) == BPF_DIV; > + bool is_sdiv = isdiv && insn->off == 1; > + bool is_smod = !isdiv && insn->off == 1; > struct bpf_insn *patchlet; > struct bpf_insn chk_and_div[] = { > /* [R,W]x div 0 -> 0 */ > @@ -20525,10 +20558,53 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > BPF_JMP_IMM(BPF_JA, 0, 0, 1), > BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > }; > + struct bpf_insn chk_and_sdiv[] = { > + /* [R,W]x sdiv 0 -> 0 */ > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > + BPF_JNE | BPF_K, insn->src_reg, > + 0, 2, 0), > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > + /* LLONG_MIN sdiv -1 -> LLONG_MIN > + * INT_MIN sdiv -1 -> INT_MIN > + */ > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > + BPF_JNE | BPF_K, insn->src_reg, > + 0, 2, -1), > + /* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */ > + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > + 0, 0, 0), > + BPF_JMP_IMM(BPF_JA, 0, 0, 1), I don't know how much it actually matters, but it feels like common safe case should be as straight-line-executed as possible, no? So maybe it's better to rearrange to roughly this (where rX is the divisor register): if rX == 0 goto L1 if rX == -1 goto L2 rY /= rX goto L3 L1: /* zero case */ rY = 0 /* fallthrough, negation doesn't hurt, but less jumping */ L2: /* negative one case (or zero) */ rY = -rY L3: ... the rest of the program code ... Those two branches for common case are still annoyingly inefficient, I wonder if we should do rX += 1 /* [-1, 0] -> [0, 1] if rX <=(unsigned) 1 goto L1 rX -= 1 /* restore original divisor */ rY /= rX /* common case */ goto L3 L1: if rX == 0 goto L2 /* jump if originally -1 */ rY = 0 /* division by zero case */ L2: /* fallthrough */ rY = -rY rX -= 1 /* restore original divisor */ L3: ... continue with the rest ... It's a bit trickier to follow, but should be faster in a common case. WDYT? Too much too far? > + *insn, > + }; > + struct bpf_insn chk_and_smod[] = { > + /* [R,W]x mod 0 -> [R,W]x */ > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > + BPF_JNE | BPF_K, insn->src_reg, > + 0, 2, 0), > + BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > + /* [R,W]x mod -1 -> 0 */ > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > + BPF_JNE | BPF_K, insn->src_reg, > + 0, 2, -1), > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > + *insn, > + }; > Same idea here, keep the common case as straight as possible. > - patchlet = isdiv ? chk_and_div : chk_and_mod; > - cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > - ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > + if (is_sdiv) { > + patchlet = chk_and_sdiv; > + cnt = ARRAY_SIZE(chk_and_sdiv); > + } else if (is_smod) { > + patchlet = chk_and_smod; > + cnt = ARRAY_SIZE(chk_and_smod); > + } else { > + patchlet = isdiv ? chk_and_div : chk_and_mod; > + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > + ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > + } > > new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > if (!new_prog) > -- > 2.43.5 >
On Thu, Sep 12, 2024 at 11:17 AM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Wed, Sep 11, 2024 at 9:00 PM Yonghong Song <yonghong.song@linux.dev> wrote: > > > > Zac Ecob reported a problem where a bpf program may cause kernel crash due > > to the following error: > > Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI > > > > The failure is due to the below signed divide: > > LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808. > > LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808, > > but it is impossible since for 64-bit system, the maximum positive > > number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will > > cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is > > LLONG_MIN. > > > > Further investigation found all the following sdiv/smod cases may trigger > > an exception when bpf program is running on x86_64 platform: > > - LLONG_MIN/-1 for 64bit operation > > - INT_MIN/-1 for 32bit operation > > - LLONG_MIN%-1 for 64bit operation > > - INT_MIN%-1 for 32bit operation > > where -1 can be an immediate or in a register. > > > > On arm64, there are no exceptions: > > - LLONG_MIN/-1 = LLONG_MIN > > - INT_MIN/-1 = INT_MIN > > - LLONG_MIN%-1 = 0 > > - INT_MIN%-1 = 0 > > where -1 can be an immediate or in a register. > > > > Insn patching is needed to handle the above cases and the patched codes > > produced results aligned with above arm64 result. > > > > [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/ > > > > Reported-by: Zac Ecob <zacecob@protonmail.com> > > Signed-off-by: Yonghong Song <yonghong.song@linux.dev> > > --- > > kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++++++--- > > 1 file changed, 80 insertions(+), 4 deletions(-) > > > > Changelogs: > > v1 -> v2: > > - Handle more crash cases like 32bit operation and modules. > > - Add more tests to test new cases. > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index f35b80c16cda..ad7f51302c70 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -20499,13 +20499,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > > /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */ > > insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code); > > > > - /* Make divide-by-zero exceptions impossible. */ > > + /* Make sdiv/smod divide-by-minus-one exceptions impossible. */ > > + if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) || > > + insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) || > > + insn->code == (BPF_ALU | BPF_MOD | BPF_K) || > > + insn->code == (BPF_ALU | BPF_DIV | BPF_K)) && > > + insn->off == 1 && insn->imm == -1) { > > + bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > > + bool isdiv = BPF_OP(insn->code) == BPF_DIV; > > + struct bpf_insn *patchlet; > > + struct bpf_insn chk_and_div[] = { > > + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > > + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > > + 0, 0, 0), > > + }; > > + struct bpf_insn chk_and_mod[] = { > > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > > + }; > > + > > + patchlet = isdiv ? chk_and_div : chk_and_mod; > > nit: "chk_and_" part in the name is misleading, it's more like > "safe_div" and "safe_mod". Oh, and it's "sdiv" and "smod" specific, so > probably not a bad idea to have that in the name as well. > > > + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : ARRAY_SIZE(chk_and_mod); > > + > > + new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > > + if (!new_prog) > > + return -ENOMEM; > > + > > + delta += cnt - 1; > > + env->prog = prog = new_prog; > > + insn = new_prog->insnsi + i + delta; > > + goto next_insn; > > + } > > + > > + /* Make divide-by-zero and divide-by-minus-one exceptions impossible. */ > > if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) || > > insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) || > > insn->code == (BPF_ALU | BPF_MOD | BPF_X) || > > insn->code == (BPF_ALU | BPF_DIV | BPF_X)) { > > bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > > bool isdiv = BPF_OP(insn->code) == BPF_DIV; > > + bool is_sdiv = isdiv && insn->off == 1; > > + bool is_smod = !isdiv && insn->off == 1; > > struct bpf_insn *patchlet; > > struct bpf_insn chk_and_div[] = { > > /* [R,W]x div 0 -> 0 */ > > @@ -20525,10 +20558,53 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > > BPF_JMP_IMM(BPF_JA, 0, 0, 1), > > BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > > }; > > + struct bpf_insn chk_and_sdiv[] = { > > + /* [R,W]x sdiv 0 -> 0 */ > > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > > + BPF_JNE | BPF_K, insn->src_reg, > > + 0, 2, 0), > > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > > + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > > + /* LLONG_MIN sdiv -1 -> LLONG_MIN > > + * INT_MIN sdiv -1 -> INT_MIN > > + */ > > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > > + BPF_JNE | BPF_K, insn->src_reg, > > + 0, 2, -1), > > + /* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */ > > + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > > + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > > + 0, 0, 0), > > + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > > I don't know how much it actually matters, but it feels like common > safe case should be as straight-line-executed as possible, no? > > So maybe it's better to rearrange to roughly this (where rX is the > divisor register): > > if rX == 0 goto L1 > if rX == -1 goto L2 > rY /= rX > goto L3 > L1: /* zero case */ > rY = 0 /* fallthrough, negation doesn't hurt, but less jumping */ > L2: /* negative one case (or zero) */ > rY = -rY > L3: > ... the rest of the program code ... > > > Those two branches for common case are still annoyingly inefficient, I > wonder if we should do > > rX += 1 /* [-1, 0] -> [0, 1] > if rX <=(unsigned) 1 goto L1 > rX -= 1 /* restore original divisor */ > rY /= rX /* common case */ > goto L3 > L1: > if rX == 0 goto L2 /* jump if originally -1 */ > rY = 0 /* division by zero case */ > L2: /* fallthrough */ > rY = -rY > rX -= 1 /* restore original divisor */ > L3: > ... continue with the rest ... hmm.. just in case rX is the same register as rY, probably best to restore rX early right at L1: label (and adjust `if rX == 0 goto L2` into `if rX != 0 goto L2`). > > > It's a bit trickier to follow, but should be faster in a common case. > > WDYT? Too much too far? > > > > + *insn, > > + }; > > + struct bpf_insn chk_and_smod[] = { > > + /* [R,W]x mod 0 -> [R,W]x */ > > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > > + BPF_JNE | BPF_K, insn->src_reg, > > + 0, 2, 0), > > + BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > > + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > > + /* [R,W]x mod -1 -> 0 */ > > + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > > + BPF_JNE | BPF_K, insn->src_reg, > > + 0, 2, -1), > > + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > > + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > > + *insn, > > + }; > > > > Same idea here, keep the common case as straight as possible. > > > - patchlet = isdiv ? chk_and_div : chk_and_mod; > > - cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > > - ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > > + if (is_sdiv) { > > + patchlet = chk_and_sdiv; > > + cnt = ARRAY_SIZE(chk_and_sdiv); > > + } else if (is_smod) { > > + patchlet = chk_and_smod; > > + cnt = ARRAY_SIZE(chk_and_smod); > > + } else { > > + patchlet = isdiv ? chk_and_div : chk_and_mod; > > + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > > + ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > > + } > > > > new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > > if (!new_prog) > > -- > > 2.43.5 > >
On 9/12/24 11:17 AM, Andrii Nakryiko wrote: > On Wed, Sep 11, 2024 at 9:00 PM Yonghong Song <yonghong.song@linux.dev> wrote: >> Zac Ecob reported a problem where a bpf program may cause kernel crash due >> to the following error: >> Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI >> >> The failure is due to the below signed divide: >> LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808. >> LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808, >> but it is impossible since for 64-bit system, the maximum positive >> number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will >> cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is >> LLONG_MIN. >> >> Further investigation found all the following sdiv/smod cases may trigger >> an exception when bpf program is running on x86_64 platform: >> - LLONG_MIN/-1 for 64bit operation >> - INT_MIN/-1 for 32bit operation >> - LLONG_MIN%-1 for 64bit operation >> - INT_MIN%-1 for 32bit operation >> where -1 can be an immediate or in a register. >> >> On arm64, there are no exceptions: >> - LLONG_MIN/-1 = LLONG_MIN >> - INT_MIN/-1 = INT_MIN >> - LLONG_MIN%-1 = 0 >> - INT_MIN%-1 = 0 >> where -1 can be an immediate or in a register. >> >> Insn patching is needed to handle the above cases and the patched codes >> produced results aligned with above arm64 result. >> >> [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/ >> >> Reported-by: Zac Ecob <zacecob@protonmail.com> >> Signed-off-by: Yonghong Song <yonghong.song@linux.dev> >> --- >> kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 80 insertions(+), 4 deletions(-) >> >> Changelogs: >> v1 -> v2: >> - Handle more crash cases like 32bit operation and modules. >> - Add more tests to test new cases. >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index f35b80c16cda..ad7f51302c70 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -20499,13 +20499,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) >> /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */ >> insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code); >> >> - /* Make divide-by-zero exceptions impossible. */ >> + /* Make sdiv/smod divide-by-minus-one exceptions impossible. */ >> + if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) || >> + insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) || >> + insn->code == (BPF_ALU | BPF_MOD | BPF_K) || >> + insn->code == (BPF_ALU | BPF_DIV | BPF_K)) && >> + insn->off == 1 && insn->imm == -1) { >> + bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; >> + bool isdiv = BPF_OP(insn->code) == BPF_DIV; >> + struct bpf_insn *patchlet; >> + struct bpf_insn chk_and_div[] = { >> + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | >> + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, >> + 0, 0, 0), >> + }; >> + struct bpf_insn chk_and_mod[] = { >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), >> + }; >> + >> + patchlet = isdiv ? chk_and_div : chk_and_mod; > nit: "chk_and_" part in the name is misleading, it's more like > "safe_div" and "safe_mod". Oh, and it's "sdiv" and "smod" specific, so > probably not a bad idea to have that in the name as well. good idea. Will use chk_and_sdiv and chk_and_smod. > >> + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : ARRAY_SIZE(chk_and_mod); >> + >> + new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); >> + if (!new_prog) >> + return -ENOMEM; >> + >> + delta += cnt - 1; >> + env->prog = prog = new_prog; >> + insn = new_prog->insnsi + i + delta; >> + goto next_insn; >> + } >> + >> + /* Make divide-by-zero and divide-by-minus-one exceptions impossible. */ >> if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) || >> insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) || >> insn->code == (BPF_ALU | BPF_MOD | BPF_X) || >> insn->code == (BPF_ALU | BPF_DIV | BPF_X)) { >> bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; >> bool isdiv = BPF_OP(insn->code) == BPF_DIV; >> + bool is_sdiv = isdiv && insn->off == 1; >> + bool is_smod = !isdiv && insn->off == 1; >> struct bpf_insn *patchlet; >> struct bpf_insn chk_and_div[] = { >> /* [R,W]x div 0 -> 0 */ >> @@ -20525,10 +20558,53 @@ static int do_misc_fixups(struct bpf_verifier_env *env) >> BPF_JMP_IMM(BPF_JA, 0, 0, 1), >> BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), >> }; >> + struct bpf_insn chk_and_sdiv[] = { >> + /* [R,W]x sdiv 0 -> 0 */ >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | >> + BPF_JNE | BPF_K, insn->src_reg, >> + 0, 2, 0), >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), >> + BPF_JMP_IMM(BPF_JA, 0, 0, 4), >> + /* LLONG_MIN sdiv -1 -> LLONG_MIN >> + * INT_MIN sdiv -1 -> INT_MIN >> + */ >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | >> + BPF_JNE | BPF_K, insn->src_reg, >> + 0, 2, -1), >> + /* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */ >> + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | >> + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, >> + 0, 0, 0), >> + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > I don't know how much it actually matters, but it feels like common > safe case should be as straight-line-executed as possible, no? > > So maybe it's better to rearrange to roughly this (where rX is the > divisor register): > > if rX == 0 goto L1 > if rX == -1 goto L2 > rY /= rX > goto L3 > L1: /* zero case */ > rY = 0 /* fallthrough, negation doesn't hurt, but less jumping */ > L2: /* negative one case (or zero) */ > rY = -rY > L3: > ... the rest of the program code ... My previous patched insn try to clearly separate rX == 0 and rX == -1 case. It has 2 insns including 2 cond jmps, 2 uncond jmps and one 3 alu operations. The above one removed one uncond jmp, which is indeed better. > > > Those two branches for common case are still annoyingly inefficient, I > wonder if we should do > > rX += 1 /* [-1, 0] -> [0, 1] > if rX <=(unsigned) 1 goto L1 > rX -= 1 /* restore original divisor */ > rY /= rX /* common case */ > goto L3 > L1: > if rX == 0 goto L2 /* jump if originally -1 */ > rY = 0 /* division by zero case */ > L2: /* fallthrough */ > rY = -rY > rX -= 1 /* restore original divisor */ > L3: > ... continue with the rest ... > > > It's a bit trickier to follow, but should be faster in a common case. > > WDYT? Too much too far? This is even better. The above rX -= 1 can be removed if we use BPF_REG_AX as the temporary register. For example, tmp = rX tmp += 1 /* [-1, 0] -> [0, 1] if tmp <=(unsigned) 1 goto L1 rY /= rX /* common case */ goto L3 L1: if tmp == 0 goto L2 /* jump if originally -1 */ rY = 0 /* division by zero case */ L2: /* fallthrough */ rY = -rY L3: ... continue with the rest ... Maybe we can do even better tmp = rX tmp += 1 /* [-1, 0] -> [0, 1] if tmp >(unsigned) 1 goto L2 if tmp == 0 goto L1 rY = 0 L1: rY = -rY; goto L3 L2: rY /= rX L3: Could this be even better by reducing one uncond jmp in the fast path? > > >> + *insn, >> + }; >> + struct bpf_insn chk_and_smod[] = { >> + /* [R,W]x mod 0 -> [R,W]x */ >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | >> + BPF_JNE | BPF_K, insn->src_reg, >> + 0, 2, 0), >> + BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), >> + BPF_JMP_IMM(BPF_JA, 0, 0, 4), >> + /* [R,W]x mod -1 -> 0 */ >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | >> + BPF_JNE | BPF_K, insn->src_reg, >> + 0, 2, -1), >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), >> + BPF_JMP_IMM(BPF_JA, 0, 0, 1), >> + *insn, >> + }; >> > Same idea here, keep the common case as straight as possible. Sure. Will do. > >> - patchlet = isdiv ? chk_and_div : chk_and_mod; >> - cnt = isdiv ? ARRAY_SIZE(chk_and_div) : >> - ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); >> + if (is_sdiv) { >> + patchlet = chk_and_sdiv; >> + cnt = ARRAY_SIZE(chk_and_sdiv); >> + } else if (is_smod) { >> + patchlet = chk_and_smod; >> + cnt = ARRAY_SIZE(chk_and_smod); >> + } else { >> + patchlet = isdiv ? chk_and_div : chk_and_mod; >> + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : >> + ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); >> + } >> >> new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); >> if (!new_prog) >> -- >> 2.43.5 >>
On Thu, Sep 12, 2024 at 3:53 PM Yonghong Song <yonghong.song@linux.dev> wrote: > > > On 9/12/24 11:17 AM, Andrii Nakryiko wrote: > > On Wed, Sep 11, 2024 at 9:00 PM Yonghong Song <yonghong.song@linux.dev> wrote: > >> Zac Ecob reported a problem where a bpf program may cause kernel crash due > >> to the following error: > >> Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI > >> > >> The failure is due to the below signed divide: > >> LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808. > >> LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808, > >> but it is impossible since for 64-bit system, the maximum positive > >> number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will > >> cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is > >> LLONG_MIN. > >> > >> Further investigation found all the following sdiv/smod cases may trigger > >> an exception when bpf program is running on x86_64 platform: > >> - LLONG_MIN/-1 for 64bit operation > >> - INT_MIN/-1 for 32bit operation > >> - LLONG_MIN%-1 for 64bit operation > >> - INT_MIN%-1 for 32bit operation > >> where -1 can be an immediate or in a register. > >> > >> On arm64, there are no exceptions: > >> - LLONG_MIN/-1 = LLONG_MIN > >> - INT_MIN/-1 = INT_MIN > >> - LLONG_MIN%-1 = 0 > >> - INT_MIN%-1 = 0 > >> where -1 can be an immediate or in a register. > >> > >> Insn patching is needed to handle the above cases and the patched codes > >> produced results aligned with above arm64 result. > >> > >> [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/ > >> > >> Reported-by: Zac Ecob <zacecob@protonmail.com> > >> Signed-off-by: Yonghong Song <yonghong.song@linux.dev> > >> --- > >> kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++++++--- > >> 1 file changed, 80 insertions(+), 4 deletions(-) > >> > >> Changelogs: > >> v1 -> v2: > >> - Handle more crash cases like 32bit operation and modules. > >> - Add more tests to test new cases. > >> > >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > >> index f35b80c16cda..ad7f51302c70 100644 > >> --- a/kernel/bpf/verifier.c > >> +++ b/kernel/bpf/verifier.c > >> @@ -20499,13 +20499,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > >> /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */ > >> insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code); > >> > >> - /* Make divide-by-zero exceptions impossible. */ > >> + /* Make sdiv/smod divide-by-minus-one exceptions impossible. */ > >> + if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) || > >> + insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) || > >> + insn->code == (BPF_ALU | BPF_MOD | BPF_K) || > >> + insn->code == (BPF_ALU | BPF_DIV | BPF_K)) && > >> + insn->off == 1 && insn->imm == -1) { > >> + bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > >> + bool isdiv = BPF_OP(insn->code) == BPF_DIV; > >> + struct bpf_insn *patchlet; > >> + struct bpf_insn chk_and_div[] = { > >> + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > >> + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > >> + 0, 0, 0), > >> + }; > >> + struct bpf_insn chk_and_mod[] = { > >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > >> + }; > >> + > >> + patchlet = isdiv ? chk_and_div : chk_and_mod; > > nit: "chk_and_" part in the name is misleading, it's more like > > "safe_div" and "safe_mod". Oh, and it's "sdiv" and "smod" specific, so > > probably not a bad idea to have that in the name as well. > > good idea. Will use chk_and_sdiv and chk_and_smod. > > > > >> + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : ARRAY_SIZE(chk_and_mod); > >> + > >> + new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > >> + if (!new_prog) > >> + return -ENOMEM; > >> + > >> + delta += cnt - 1; > >> + env->prog = prog = new_prog; > >> + insn = new_prog->insnsi + i + delta; > >> + goto next_insn; > >> + } > >> + > >> + /* Make divide-by-zero and divide-by-minus-one exceptions impossible. */ > >> if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) || > >> insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) || > >> insn->code == (BPF_ALU | BPF_MOD | BPF_X) || > >> insn->code == (BPF_ALU | BPF_DIV | BPF_X)) { > >> bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; > >> bool isdiv = BPF_OP(insn->code) == BPF_DIV; > >> + bool is_sdiv = isdiv && insn->off == 1; > >> + bool is_smod = !isdiv && insn->off == 1; > >> struct bpf_insn *patchlet; > >> struct bpf_insn chk_and_div[] = { > >> /* [R,W]x div 0 -> 0 */ > >> @@ -20525,10 +20558,53 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > >> BPF_JMP_IMM(BPF_JA, 0, 0, 1), > >> BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > >> }; > >> + struct bpf_insn chk_and_sdiv[] = { > >> + /* [R,W]x sdiv 0 -> 0 */ > >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > >> + BPF_JNE | BPF_K, insn->src_reg, > >> + 0, 2, 0), > >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > >> + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > >> + /* LLONG_MIN sdiv -1 -> LLONG_MIN > >> + * INT_MIN sdiv -1 -> INT_MIN > >> + */ > >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > >> + BPF_JNE | BPF_K, insn->src_reg, > >> + 0, 2, -1), > >> + /* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */ > >> + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | > >> + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, > >> + 0, 0, 0), > >> + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > > I don't know how much it actually matters, but it feels like common > > safe case should be as straight-line-executed as possible, no? > > > > So maybe it's better to rearrange to roughly this (where rX is the > > divisor register): > > > > if rX == 0 goto L1 > > if rX == -1 goto L2 > > rY /= rX > > goto L3 > > L1: /* zero case */ > > rY = 0 /* fallthrough, negation doesn't hurt, but less jumping */ > > L2: /* negative one case (or zero) */ > > rY = -rY > > L3: > > ... the rest of the program code ... > > My previous patched insn try to clearly separate rX == 0 and > rX == -1 case. It has 2 insns including 2 cond jmps, 2 uncond jmps and > one 3 alu operations. The above one removed one uncond jmp, which > is indeed better. > > > > > > > Those two branches for common case are still annoyingly inefficient, I > > wonder if we should do > > > > rX += 1 /* [-1, 0] -> [0, 1] > > if rX <=(unsigned) 1 goto L1 > > rX -= 1 /* restore original divisor */ > > rY /= rX /* common case */ > > goto L3 > > L1: > > if rX == 0 goto L2 /* jump if originally -1 */ > > rY = 0 /* division by zero case */ > > L2: /* fallthrough */ > > rY = -rY > > rX -= 1 /* restore original divisor */ > > L3: > > ... continue with the rest ... > > > > > > It's a bit trickier to follow, but should be faster in a common case. > > > > WDYT? Too much too far? > > This is even better. The above rX -= 1 can be removed if we use > BPF_REG_AX as the temporary register. For example, > > tmp = rX > tmp += 1 /* [-1, 0] -> [0, 1] > if tmp <=(unsigned) 1 goto L1 > rY /= rX /* common case */ > goto L3 > L1: > if tmp == 0 goto L2 /* jump if originally -1 */ > rY = 0 /* division by zero case */ > L2: /* fallthrough */ > rY = -rY > L3: > ... continue with the rest ... > > Maybe we can do even better > > tmp = rX > tmp += 1 /* [-1, 0] -> [0, 1] > if tmp >(unsigned) 1 goto L2 > if tmp == 0 goto L1 > rY = 0 > L1: > rY = -rY; > goto L3 > L2: > rY /= rX > L3: > > Could this be even better by reducing one uncond jmp in the fast path? Yep, makes sense to me. Go for it (as far as I'm concerned). > > > > > > >> + *insn, > >> + }; > >> + struct bpf_insn chk_and_smod[] = { > >> + /* [R,W]x mod 0 -> [R,W]x */ > >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > >> + BPF_JNE | BPF_K, insn->src_reg, > >> + 0, 2, 0), > >> + BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), > >> + BPF_JMP_IMM(BPF_JA, 0, 0, 4), > >> + /* [R,W]x mod -1 -> 0 */ > >> + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | > >> + BPF_JNE | BPF_K, insn->src_reg, > >> + 0, 2, -1), > >> + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), > >> + BPF_JMP_IMM(BPF_JA, 0, 0, 1), > >> + *insn, > >> + }; > >> > > Same idea here, keep the common case as straight as possible. > > Sure. Will do. > > > > >> - patchlet = isdiv ? chk_and_div : chk_and_mod; > >> - cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > >> - ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > >> + if (is_sdiv) { > >> + patchlet = chk_and_sdiv; > >> + cnt = ARRAY_SIZE(chk_and_sdiv); > >> + } else if (is_smod) { > >> + patchlet = chk_and_smod; > >> + cnt = ARRAY_SIZE(chk_and_smod); > >> + } else { > >> + patchlet = isdiv ? chk_and_div : chk_and_mod; > >> + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : > >> + ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); > >> + } > >> > >> new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); > >> if (!new_prog) > >> -- > >> 2.43.5 > >>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f35b80c16cda..ad7f51302c70 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -20499,13 +20499,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) /* Convert BPF_CLASS(insn->code) == BPF_ALU64 to 32-bit ALU */ insn->code = BPF_ALU | BPF_OP(insn->code) | BPF_SRC(insn->code); - /* Make divide-by-zero exceptions impossible. */ + /* Make sdiv/smod divide-by-minus-one exceptions impossible. */ + if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) || + insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) || + insn->code == (BPF_ALU | BPF_MOD | BPF_K) || + insn->code == (BPF_ALU | BPF_DIV | BPF_K)) && + insn->off == 1 && insn->imm == -1) { + bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; + bool isdiv = BPF_OP(insn->code) == BPF_DIV; + struct bpf_insn *patchlet; + struct bpf_insn chk_and_div[] = { + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, + 0, 0, 0), + }; + struct bpf_insn chk_and_mod[] = { + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), + }; + + patchlet = isdiv ? chk_and_div : chk_and_mod; + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : ARRAY_SIZE(chk_and_mod); + + new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); + if (!new_prog) + return -ENOMEM; + + delta += cnt - 1; + env->prog = prog = new_prog; + insn = new_prog->insnsi + i + delta; + goto next_insn; + } + + /* Make divide-by-zero and divide-by-minus-one exceptions impossible. */ if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) || insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) || insn->code == (BPF_ALU | BPF_MOD | BPF_X) || insn->code == (BPF_ALU | BPF_DIV | BPF_X)) { bool is64 = BPF_CLASS(insn->code) == BPF_ALU64; bool isdiv = BPF_OP(insn->code) == BPF_DIV; + bool is_sdiv = isdiv && insn->off == 1; + bool is_smod = !isdiv && insn->off == 1; struct bpf_insn *patchlet; struct bpf_insn chk_and_div[] = { /* [R,W]x div 0 -> 0 */ @@ -20525,10 +20558,53 @@ static int do_misc_fixups(struct bpf_verifier_env *env) BPF_JMP_IMM(BPF_JA, 0, 0, 1), BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), }; + struct bpf_insn chk_and_sdiv[] = { + /* [R,W]x sdiv 0 -> 0 */ + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | + BPF_JNE | BPF_K, insn->src_reg, + 0, 2, 0), + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), + BPF_JMP_IMM(BPF_JA, 0, 0, 4), + /* LLONG_MIN sdiv -1 -> LLONG_MIN + * INT_MIN sdiv -1 -> INT_MIN + */ + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | + BPF_JNE | BPF_K, insn->src_reg, + 0, 2, -1), + /* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */ + BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) | + BPF_OP(BPF_NEG) | BPF_K, insn->dst_reg, + 0, 0, 0), + BPF_JMP_IMM(BPF_JA, 0, 0, 1), + *insn, + }; + struct bpf_insn chk_and_smod[] = { + /* [R,W]x mod 0 -> [R,W]x */ + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | + BPF_JNE | BPF_K, insn->src_reg, + 0, 2, 0), + BPF_MOV32_REG(insn->dst_reg, insn->dst_reg), + BPF_JMP_IMM(BPF_JA, 0, 0, 4), + /* [R,W]x mod -1 -> 0 */ + BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) | + BPF_JNE | BPF_K, insn->src_reg, + 0, 2, -1), + BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg), + BPF_JMP_IMM(BPF_JA, 0, 0, 1), + *insn, + }; - patchlet = isdiv ? chk_and_div : chk_and_mod; - cnt = isdiv ? ARRAY_SIZE(chk_and_div) : - ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); + if (is_sdiv) { + patchlet = chk_and_sdiv; + cnt = ARRAY_SIZE(chk_and_sdiv); + } else if (is_smod) { + patchlet = chk_and_smod; + cnt = ARRAY_SIZE(chk_and_smod); + } else { + patchlet = isdiv ? chk_and_div : chk_and_mod; + cnt = isdiv ? ARRAY_SIZE(chk_and_div) : + ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0); + } new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt); if (!new_prog)
Zac Ecob reported a problem where a bpf program may cause kernel crash due to the following error: Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI The failure is due to the below signed divide: LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808. LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808, but it is impossible since for 64-bit system, the maximum positive number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is LLONG_MIN. Further investigation found all the following sdiv/smod cases may trigger an exception when bpf program is running on x86_64 platform: - LLONG_MIN/-1 for 64bit operation - INT_MIN/-1 for 32bit operation - LLONG_MIN%-1 for 64bit operation - INT_MIN%-1 for 32bit operation where -1 can be an immediate or in a register. On arm64, there are no exceptions: - LLONG_MIN/-1 = LLONG_MIN - INT_MIN/-1 = INT_MIN - LLONG_MIN%-1 = 0 - INT_MIN%-1 = 0 where -1 can be an immediate or in a register. Insn patching is needed to handle the above cases and the patched codes produced results aligned with above arm64 result. [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/ Reported-by: Zac Ecob <zacecob@protonmail.com> Signed-off-by: Yonghong Song <yonghong.song@linux.dev> --- kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 80 insertions(+), 4 deletions(-) Changelogs: v1 -> v2: - Handle more crash cases like 32bit operation and modules. - Add more tests to test new cases.