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 <[email protected]> > --- > 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 > [...]
