| Message ID | 20231101-fix-check-stack-write-v2-1-cb7c17b869b0@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 811c363645b33e6e22658634329e95f383dfc705 |
| Headers | show |
| Series | bpf: Fix incorrect immediate spill | expand |
On Wed, Nov 01, 2023 at 08:33:22AM +0100, Hao Sun wrote: > In check_stack_write_fixed_off(), imm value is cast to u32 before being > spilled to the stack. Therefore, the sign information is lost, and the > range information is incorrect when load from the stack again. > > For the following prog: > 0: r2 = r10 > 1: *(u64*)(r2 -40) = -44 > 2: r0 = *(u64*)(r2 - 40) > 3: if r0 s<= 0xa goto +2 > 4: r0 = 1 > 5: exit > 6: r0 = 0 > 7: exit > > The verifier gives: > func#0 @0 > 0: R1=ctx(off=0,imm=0) R10=fp0 > 0: (bf) r2 = r10 ; R2_w=fp0 R10=fp0 > 1: (7a) *(u64 *)(r2 -40) = -44 ; R2_w=fp0 fp-40_w=4294967252 > 2: (79) r0 = *(u64 *)(r2 -40) ; R0_w=4294967252 R2_w=fp0 > fp-40_w=4294967252 > 3: (c5) if r0 s< 0xa goto pc+2 > mark_precise: frame0: last_idx 3 first_idx 0 subseq_idx -1 > mark_precise: frame0: regs=r0 stack= before 2: (79) r0 = *(u64 *)(r2 -40) > 3: R0_w=4294967252 > 4: (b7) r0 = 1 ; R0_w=1 > 5: (95) exit > verification time 7971 usec > stack depth 40 > processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 > peak_states 0 mark_read 0 > > So remove the incorrect cast, since imm field is declared as s32, and > __mark_reg_known() takes u64, so imm would be correctly sign extended > by compiler. > > Fixes: ecdf985d7615 ("bpf: track immediate values written to stack by BPF_ST instruction") > Cc: stable@vger.kernel.org > Signed-off-by: Hao Sun <sunhao.th@gmail.com> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
On Wed, 2023-11-01 at 08:33 +0100, Hao Sun wrote: > In check_stack_write_fixed_off(), imm value is cast to u32 before being > spilled to the stack. Therefore, the sign information is lost, and the > range information is incorrect when load from the stack again. > > For the following prog: > 0: r2 = r10 > 1: *(u64*)(r2 -40) = -44 > 2: r0 = *(u64*)(r2 - 40) > 3: if r0 s<= 0xa goto +2 > 4: r0 = 1 > 5: exit > 6: r0 = 0 > 7: exit > > The verifier gives: > func#0 @0 > 0: R1=ctx(off=0,imm=0) R10=fp0 > 0: (bf) r2 = r10 ; R2_w=fp0 R10=fp0 > 1: (7a) *(u64 *)(r2 -40) = -44 ; R2_w=fp0 fp-40_w=4294967252 > 2: (79) r0 = *(u64 *)(r2 -40) ; R0_w=4294967252 R2_w=fp0 > fp-40_w=4294967252 > 3: (c5) if r0 s< 0xa goto pc+2 > mark_precise: frame0: last_idx 3 first_idx 0 subseq_idx -1 > mark_precise: frame0: regs=r0 stack= before 2: (79) r0 = *(u64 *)(r2 -40) > 3: R0_w=4294967252 > 4: (b7) r0 = 1 ; R0_w=1 > 5: (95) exit > verification time 7971 usec > stack depth 40 > processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 > peak_states 0 mark_read 0 > > So remove the incorrect cast, since imm field is declared as s32, and > __mark_reg_known() takes u64, so imm would be correctly sign extended > by compiler. > > Fixes: ecdf985d7615 ("bpf: track immediate values written to stack by BPF_ST instruction") > Cc: stable@vger.kernel.org > Signed-off-by: Hao Sun <sunhao.th@gmail.com> Acked-by: Eduard Zingerman <eddyz87@gmail.com> > --- > kernel/bpf/verifier.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 857d76694517..44af69ce1301 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -4674,7 +4674,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env, > insn->imm != 0 && env->bpf_capable) { > struct bpf_reg_state fake_reg = {}; > > - __mark_reg_known(&fake_reg, (u32)insn->imm); > + __mark_reg_known(&fake_reg, insn->imm); > fake_reg.type = SCALAR_VALUE; > save_register_state(state, spi, &fake_reg, size); > } else if (reg && is_spillable_regtype(reg->type)) { >
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 857d76694517..44af69ce1301 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4674,7 +4674,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env, insn->imm != 0 && env->bpf_capable) { struct bpf_reg_state fake_reg = {}; - __mark_reg_known(&fake_reg, (u32)insn->imm); + __mark_reg_known(&fake_reg, insn->imm); fake_reg.type = SCALAR_VALUE; save_register_state(state, spi, &fake_reg, size); } else if (reg && is_spillable_regtype(reg->type)) {
In check_stack_write_fixed_off(), imm value is cast to u32 before being spilled to the stack. Therefore, the sign information is lost, and the range information is incorrect when load from the stack again. For the following prog: 0: r2 = r10 1: *(u64*)(r2 -40) = -44 2: r0 = *(u64*)(r2 - 40) 3: if r0 s<= 0xa goto +2 4: r0 = 1 5: exit 6: r0 = 0 7: exit The verifier gives: func#0 @0 0: R1=ctx(off=0,imm=0) R10=fp0 0: (bf) r2 = r10 ; R2_w=fp0 R10=fp0 1: (7a) *(u64 *)(r2 -40) = -44 ; R2_w=fp0 fp-40_w=4294967252 2: (79) r0 = *(u64 *)(r2 -40) ; R0_w=4294967252 R2_w=fp0 fp-40_w=4294967252 3: (c5) if r0 s< 0xa goto pc+2 mark_precise: frame0: last_idx 3 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r0 stack= before 2: (79) r0 = *(u64 *)(r2 -40) 3: R0_w=4294967252 4: (b7) r0 = 1 ; R0_w=1 5: (95) exit verification time 7971 usec stack depth 40 processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0 So remove the incorrect cast, since imm field is declared as s32, and __mark_reg_known() takes u64, so imm would be correctly sign extended by compiler. Fixes: ecdf985d7615 ("bpf: track immediate values written to stack by BPF_ST instruction") Cc: stable@vger.kernel.org Signed-off-by: Hao Sun <sunhao.th@gmail.com> --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)