On Mon, Jan 8, 2024 at 12:53 PM Maxim Mikityanskiy <maxtram95@xxxxxxxxx> wrote:
>
> From: Maxim Mikityanskiy <maxim@xxxxxxxxxxxxx>
>
> The previous commit allowed to preserve boundaries and track IDs of
> scalars on narrowing fills. Add test cases for that pattern.
>
> Signed-off-by: Maxim Mikityanskiy <maxim@xxxxxxxxxxxxx>
> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> .../selftests/bpf/progs/verifier_spill_fill.c | 108 ++++++++++++++++++
> 1 file changed, 108 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> index fab8ae9fe947..3764111d190d 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> @@ -936,4 +936,112 @@ l0_%=: r0 = 0; \
> : __clobber_all);
> }
>
> +SEC("xdp")
> +__description("32-bit fill after 64-bit spill")
> +__success __retval(0)
> +__naked void fill_32bit_after_spill_64bit(void)
I guess these tests are an answer for my question about mixing
spill/fill sizes on earlier patch (so disregard those)
> +{
> + asm volatile(" \
> + /* Randomize the upper 32 bits. */ \
> + call %[bpf_get_prandom_u32]; \
> + r0 <<= 32; \
> + /* 64-bit spill r0 to stack. */ \
> + *(u64*)(r10 - 8) = r0; \
> + /* 32-bit fill r0 from stack. */ \
> + r0 = *(u32*)(r10 - %[offset]); \
have you considered doing the BYTE_ORDER check right here and have
offset embedded in assembly instruction directly:
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
r0 = *(u32*)(r10 - 8);
#else
r0 = *(u32*)(r10 - 4);
#endif
It's a bit less jumping around the code when reading. And it's kind of
obviously that this is endianness-dependent without jumping to
definition of %[offset]?
> + /* Boundary check on r0 with predetermined result. */\
> + if r0 == 0 goto l0_%=; \
> + /* Dead branch: the verifier should prune it. Do an invalid memory\
> + * access if the verifier follows it. \
> + */ \
> + r0 = *(u64*)(r9 + 0); \
> +l0_%=: exit; \
> +" :
> + : __imm(bpf_get_prandom_u32),
> +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> + __imm_const(offset, 8)
> +#else
> + __imm_const(offset, 4)
> +#endif
> + : __clobber_all);
> +}
> +
[...]
