| Message ID | 20231220214013.3327288-13-maxtram95@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Improvements for tracking scalars in the BPF verifier | expand |
On Wed, Dec 20, 2023 at 11:40:10PM +0200, Maxim Mikityanskiy wrote: > When the width of a fill is smaller than the width of the preceding > spill, the information about scalar boundaries can still be preserved, > as long as it's coerced to the right width (done by coerce_reg_to_size). > Even further, if the actual value fits into the fill width, the ID can > be preserved as well for further tracking of equal scalars. > > Implement the above improvements, which makes narrowing fills behave the > same as narrowing spills and MOVs between registers. > > Two tests are adjusted to accommodate for endianness differences and to > take into account that it's now allowed to do a narrowing fill from the > least significant bits. > > reg_bounds_sync is added to coerce_reg_to_size to correctly adjust > umin/umax boundaries after the var_off truncation, for example, a 64-bit > value 0xXXXXXXXX00000000, when read as a 32-bit, gets umin = 0, umax = > 0xFFFFFFFF, var_off = (0x0; 0xffffffff00000000), which needs to be > synced down to umax = 0, otherwise reg_bounds_sanity_check doesn't pass. > > Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com> > --- > kernel/bpf/verifier.c | 20 ++++++++++--- > .../selftests/bpf/progs/verifier_spill_fill.c | 28 +++++++++++++------ > 2 files changed, 35 insertions(+), 13 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 9b5053389739..b6e252539e52 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -4772,7 +4772,13 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env, > if (dst_regno < 0) > return 0; > > - if (!(off % BPF_REG_SIZE) && size == spill_size) { > + if (size <= spill_size && > +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ > + !(off % BPF_REG_SIZE) > +#else > + !((off + size - spill_size) % BPF_REG_SIZE) > +#endif If I understand correctly, it is preferred to keep endianess checking macro out of verfier.c and have helper function handle them instead. E.g. See bpf_ctx_narrow_access_offset() from include/linux/filter.h > [...]
On Thu, 04 Jan 2024 at 04:27:00 +0200, Eduard Zingerman wrote: > On Wed, 2023-12-20 at 23:40 +0200, Maxim Mikityanskiy wrote: > > [...] > > The two tests below were added by the following commit: > ef979017b837 ("bpf: selftest: Add verifier tests for <8-byte scalar spill and refill") > > As far as I understand, the original intent was to check the behavior > for stack read/write with non-matching size. > I think these tests are redundant after patch #13. Wdyt? _6_offset_to_skb_data is for sure not redundant. I don't test a partial fill from the most significant bits in my patch 13. u16_offset_to_skb_data is somewhat similar to fill_32bit_after_spill_64bit, but they aren't exactly the same: the former spills (u32)20 and fills (u16)20 (the same value), while my test spills (u64)0xXXXXXXXX00000000 and fills (u32)0 (the most significant bits are stripped). Maybe u16_offset_to_skb_data is redundant, but more coverage is better than less coverage, isn't it? > > diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c > > index 809a09732168..de03e72e07a9 100644 > > --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c > > +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c > > @@ -217,7 +217,7 @@ __naked void uninit_u32_from_the_stack(void) > > > > SEC("tc") > > __description("Spill a u32 const scalar. Refill as u16. Offset to skb->data") > > -__failure __msg("invalid access to packet") > > +__success __retval(0) > > __naked void u16_offset_to_skb_data(void) > > { > > asm volatile (" \ > > @@ -225,19 +225,24 @@ __naked void u16_offset_to_skb_data(void) > > r3 = *(u32*)(r1 + %[__sk_buff_data_end]); \ > > w4 = 20; \ > > *(u32*)(r10 - 8) = r4; \ > > - r4 = *(u16*)(r10 - 8); \ > > + r4 = *(u16*)(r10 - %[offset]); \ > > r0 = r2; \ > > - /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=umax=65535 */\ > > + /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=20 */\ > > r0 += r4; \ > > - /* if (r0 > r3) R0=pkt,umax=65535 R2=pkt R3=pkt_end R4=umax=65535 */\ > > + /* if (r0 > r3) R0=pkt,off=20 R2=pkt R3=pkt_end R4=20 */\ > > if r0 > r3 goto l0_%=; \ > > - /* r0 = *(u32 *)r2 R0=pkt,umax=65535 R2=pkt R3=pkt_end R4=20 */\ > > + /* r0 = *(u32 *)r2 R0=pkt,off=20 R2=pkt R3=pkt_end R4=20 */\ > > r0 = *(u32*)(r2 + 0); \ > > l0_%=: r0 = 0; \ > > exit; \ > > " : > > : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), > > - __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)) > > + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)), > > +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ > > + __imm_const(offset, 8) > > +#else > > + __imm_const(offset, 6) > > +#endif > > : __clobber_all); > > } > > > > @@ -270,7 +275,7 @@ l0_%=: r0 = 0; \ > > } > > > > SEC("tc") > > -__description("Spill a u32 const scalar. Refill as u16 from fp-6. Offset to skb->data") > > +__description("Spill a u32 const scalar. Refill as u16 from MSB. Offset to skb->data") > > __failure __msg("invalid access to packet") > > __naked void _6_offset_to_skb_data(void) > > { > > @@ -279,7 +284,7 @@ __naked void _6_offset_to_skb_data(void) > > r3 = *(u32*)(r1 + %[__sk_buff_data_end]); \ > > w4 = 20; \ > > *(u32*)(r10 - 8) = r4; \ > > - r4 = *(u16*)(r10 - 6); \ > > + r4 = *(u16*)(r10 - %[offset]); \ > > r0 = r2; \ > > /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=umax=65535 */\ > > r0 += r4; \ > > @@ -291,7 +296,12 @@ l0_%=: r0 = 0; \ > > exit; \ > > " : > > : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), > > - __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)) > > + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)), > > +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ > > + __imm_const(offset, 6) > > +#else > > + __imm_const(offset, 8) > > +#endif > > : __clobber_all); > > } > > > > >
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9b5053389739..b6e252539e52 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4772,7 +4772,13 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env, if (dst_regno < 0) return 0; - if (!(off % BPF_REG_SIZE) && size == spill_size) { + if (size <= spill_size && +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ + !(off % BPF_REG_SIZE) +#else + !((off + size - spill_size) % BPF_REG_SIZE) +#endif + ) { /* The earlier check_reg_arg() has decided the * subreg_def for this insn. Save it first. */ @@ -4780,6 +4786,12 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env, copy_register_state(&state->regs[dst_regno], reg); state->regs[dst_regno].subreg_def = subreg_def; + + /* Break the relation on a narrowing fill. + * coerce_reg_to_size will adjust the boundaries. + */ + if (get_reg_width(reg) > size * BITS_PER_BYTE) + state->regs[dst_regno].id = 0; } else { int spill_cnt = 0, zero_cnt = 0; @@ -6055,10 +6067,10 @@ static void coerce_reg_to_size(struct bpf_reg_state *reg, int size) * values are also truncated so we push 64-bit bounds into * 32-bit bounds. Above were truncated < 32-bits already. */ - if (size < 4) { + if (size < 4) __mark_reg32_unbounded(reg); - reg_bounds_sync(reg); - } + + reg_bounds_sync(reg); } static void set_sext64_default_val(struct bpf_reg_state *reg, int size) diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c index 809a09732168..de03e72e07a9 100644 --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c @@ -217,7 +217,7 @@ __naked void uninit_u32_from_the_stack(void) SEC("tc") __description("Spill a u32 const scalar. Refill as u16. Offset to skb->data") -__failure __msg("invalid access to packet") +__success __retval(0) __naked void u16_offset_to_skb_data(void) { asm volatile (" \ @@ -225,19 +225,24 @@ __naked void u16_offset_to_skb_data(void) r3 = *(u32*)(r1 + %[__sk_buff_data_end]); \ w4 = 20; \ *(u32*)(r10 - 8) = r4; \ - r4 = *(u16*)(r10 - 8); \ + r4 = *(u16*)(r10 - %[offset]); \ r0 = r2; \ - /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=umax=65535 */\ + /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=20 */\ r0 += r4; \ - /* if (r0 > r3) R0=pkt,umax=65535 R2=pkt R3=pkt_end R4=umax=65535 */\ + /* if (r0 > r3) R0=pkt,off=20 R2=pkt R3=pkt_end R4=20 */\ if r0 > r3 goto l0_%=; \ - /* r0 = *(u32 *)r2 R0=pkt,umax=65535 R2=pkt R3=pkt_end R4=20 */\ + /* r0 = *(u32 *)r2 R0=pkt,off=20 R2=pkt R3=pkt_end R4=20 */\ r0 = *(u32*)(r2 + 0); \ l0_%=: r0 = 0; \ exit; \ " : : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), - __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)) + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)), +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ + __imm_const(offset, 8) +#else + __imm_const(offset, 6) +#endif : __clobber_all); } @@ -270,7 +275,7 @@ l0_%=: r0 = 0; \ } SEC("tc") -__description("Spill a u32 const scalar. Refill as u16 from fp-6. Offset to skb->data") +__description("Spill a u32 const scalar. Refill as u16 from MSB. Offset to skb->data") __failure __msg("invalid access to packet") __naked void _6_offset_to_skb_data(void) { @@ -279,7 +284,7 @@ __naked void _6_offset_to_skb_data(void) r3 = *(u32*)(r1 + %[__sk_buff_data_end]); \ w4 = 20; \ *(u32*)(r10 - 8) = r4; \ - r4 = *(u16*)(r10 - 6); \ + r4 = *(u16*)(r10 - %[offset]); \ r0 = r2; \ /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=umax=65535 */\ r0 += r4; \ @@ -291,7 +296,12 @@ l0_%=: r0 = 0; \ exit; \ " : : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), - __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)) + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)), +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ + __imm_const(offset, 6) +#else + __imm_const(offset, 8) +#endif : __clobber_all); }