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Message-ID: <CAEf4BzaQzWLJqMuOtBX+wmH4EH43nYjTcuVun5nGUwEY_6E7RA@mail.gmail.com>
Date: Tue, 9 Jan 2024 16:27:38 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Maxim Mikityanskiy <maxtram95@...il.com>
Cc: Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Shung-Hsi Yu <shung-hsi.yu@...e.com>, John Fastabend <john.fastabend@...il.com>,
Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Jesper Dangaard Brouer <hawk@...nel.org>, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 15/15] selftests/bpf: states pruning checks
for scalar vs STACK_{MISC,ZERO}
On Mon, Jan 8, 2024 at 12:53 PM Maxim Mikityanskiy <maxtram95@...il.com> wrote:
>
> From: Eduard Zingerman <eddyz87@...il.com>
>
> Check that stacksafe() considers the following old vs cur stack spill
> state combinations equivalent:
> - spill of unbound scalar vs combination of STACK_{MISC,ZERO,INVALID}
> - STACK_MISC vs spill of unbound scalar
> - spill of scalar 0 vs STACK_ZERO
> - STACK_ZERO vs spill of scalar 0
>
> Signed-off-by: Eduard Zingerman <eddyz87@...il.com>
> ---
> .../selftests/bpf/progs/verifier_spill_fill.c | 192 ++++++++++++++++++
> 1 file changed, 192 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> index 3764111d190d..3cd3fe30357f 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
> @@ -1044,4 +1044,196 @@ l0_%=: r1 >>= 32; \
> : __clobber_all);
> }
>
> +/* stacksafe(): check if spill of unbound scalar in old state is
> + * considered equivalent to any state of the spill in the current state.
> + *
> + * On the first verification path an unbound scalar is written for
> + * fp-8 and later marked precise.
> + * On the second verification path a mix of STACK_MISC/ZERO/INVALID is
> + * written to fp-8. These should be considered equivalent.
> + */
> +SEC("socket")
> +__success __log_level(2)
> +__msg("10: (79) r0 = *(u64 *)(r10 -8)")
> +__msg("10: safe")
> +__msg("processed 16 insns")
> +__flag(BPF_F_TEST_STATE_FREQ)
> +__naked void old_unbound_scalar_vs_cur_anything(void)
> +{
> + asm volatile(
> + /* get a random value for branching */
> + "call %[bpf_ktime_get_ns];"
> + "r7 = r0;"
> + /* get a random value for storing at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "if r7 == 0 goto 1f;"
> + /* unbound scalar written to fp-8 */
> + "*(u64*)(r10 - 8) = r0;"
> + "goto 2f;"
> +"1:"
> + /* mark fp-8 as mix of STACK_MISC/ZERO/INVALID */
> + "r1 = 0;"
> + "*(u8*)(r10 - 8) = r0;"
this is actually a spilled register, not STACK_ZERO. Is it important?
> + "*(u8*)(r10 - 7) = r1;"
> + /* fp-2..fp-6 remain STACK_INVALID */
> + "*(u8*)(r10 - 1) = r0;"
> +"2:"
> + /* read fp-8 and force it precise, should be considered safe
> + * on second visit
> + */
> + "r0 = *(u64*)(r10 - 8);"
> + "r0 &= 0xff;"
> + "r1 = r10;"
> + "r1 += r0;"
> + "exit;"
> + :
> + : __imm(bpf_ktime_get_ns)
> + : __clobber_all);
> +}
> +
> +/* stacksafe(): check if STACK_MISC in old state is considered
> + * equivalent to stack spill of unbound scalar in cur state.
> + */
> +SEC("socket")
> +__success __log_level(2)
> +__msg("8: (79) r0 = *(u64 *)(r10 -8) ; R0_w=scalar(id=1) R10=fp0 fp-8=scalar(id=1)")
> +__msg("8: safe")
> +__msg("processed 11 insns")
> +__flag(BPF_F_TEST_STATE_FREQ)
> +__naked void old_unbound_scalar_vs_cur_stack_misc(void)
> +{
> + asm volatile(
> + /* get a random value for branching */
> + "call %[bpf_ktime_get_ns];"
> + "if r0 == 0 goto 1f;"
> + /* conjure unbound scalar at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "*(u64*)(r10 - 8) = r0;"
> + "goto 2f;"
> +"1:"
> + /* conjure STACK_MISC at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "*(u64*)(r10 - 8) = r0;"
> + "*(u32*)(r10 - 4) = r0;"
> +"2:"
> + /* read fp-8, should be considered safe on second visit */
> + "r0 = *(u64*)(r10 - 8);"
> + "exit;"
> + :
> + : __imm(bpf_ktime_get_ns)
> + : __clobber_all);
> +}
> +
> +/* stacksafe(): check if stack spill of unbound scalar in old state is
> + * considered equivalent to STACK_MISC in cur state.
> + */
> +SEC("socket")
> +__success __log_level(2)
> +__msg("8: (79) r0 = *(u64 *)(r10 -8) ; R0_w=scalar() R10=fp0 fp-8=mmmmmmmm")
> +__msg("8: safe")
> +__msg("processed 11 insns")
> +__flag(BPF_F_TEST_STATE_FREQ)
> +__naked void old_stack_misc_vs_cur_unbound_scalar(void)
> +{
> + asm volatile(
> + /* get a random value for branching */
> + "call %[bpf_ktime_get_ns];"
> + "if r0 == 0 goto 1f;"
> + /* conjure STACK_MISC at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "*(u64*)(r10 - 8) = r0;"
> + "*(u32*)(r10 - 4) = r0;"
> + "goto 2f;"
> +"1:"
> + /* conjure unbound scalar at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "*(u64*)(r10 - 8) = r0;"
> +"2:"
> + /* read fp-8, should be considered safe on second visit */
> + "r0 = *(u64*)(r10 - 8);"
> + "exit;"
> + :
> + : __imm(bpf_ktime_get_ns)
> + : __clobber_all);
> +}
> +
> +/* stacksafe(): check if spill of register with value 0 in old state
> + * is considered equivalent to STACK_ZERO.
> + */
> +SEC("socket")
> +__success __log_level(2)
> +__msg("9: (79) r0 = *(u64 *)(r10 -8)")
> +__msg("9: safe")
> +__msg("processed 15 insns")
> +__flag(BPF_F_TEST_STATE_FREQ)
> +__naked void old_spill_zero_vs_stack_zero(void)
> +{
> + asm volatile(
> + /* get a random value for branching */
> + "call %[bpf_ktime_get_ns];"
> + "r7 = r0;"
> + /* get a random value for storing at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "if r7 == 0 goto 1f;"
> + /* conjure spilled register with value 0 at fp-8 */
> + "*(u64*)(r10 - 8) = r0;"
> + "if r0 != 0 goto 3f;"
> + "goto 2f;"
> +"1:"
> + /* conjure STACK_ZERO at fp-8 */
> + "r1 = 0;"
> + "*(u64*)(r10 - 8) = r1;"
this is not STACK_ZERO, it's full register spill
> +"2:"
> + /* read fp-8 and force it precise, should be considered safe
> + * on second visit
> + */
> + "r0 = *(u64*)(r10 - 8);"
> + "r1 = r10;"
> + "r1 += r0;"
> +"3:"
> + "exit;"
> + :
> + : __imm(bpf_ktime_get_ns)
> + : __clobber_all);
> +}
> +
> +/* stacksafe(): similar to old_spill_zero_vs_stack_zero() but the
> + * other way around: check if STACK_ZERO is considered equivalent to
> + * spill of register with value 0.
> + */
> +SEC("socket")
> +__success __log_level(2)
> +__msg("8: (79) r0 = *(u64 *)(r10 -8)")
> +__msg("8: safe")
> +__msg("processed 14 insns")
> +__flag(BPF_F_TEST_STATE_FREQ)
> +__naked void old_stack_zero_vs_spill_zero(void)
> +{
> + asm volatile(
> + /* get a random value for branching */
> + "call %[bpf_ktime_get_ns];"
> + "if r0 == 0 goto 1f;"
> + /* conjure STACK_ZERO at fp-8 */
> + "r1 = 0;"
> + "*(u64*)(r10 - 8) = r1;"
same, please double check this STACK_xxx assumptions, as now we spill
registers instead of STACK_ZERO in a lot of cases
> + "goto 2f;"
> +"1:"
> + /* conjure spilled register with value 0 at fp-8 */
> + "call %[bpf_ktime_get_ns];"
> + "*(u64*)(r10 - 8) = r0;"
> + "if r0 != 0 goto 3f;"
> +"2:"
> + /* read fp-8 and force it precise, should be considered safe
> + * on second visit
> + */
> + "r0 = *(u64*)(r10 - 8);"
> + "r1 = r10;"
> + "r1 += r0;"
> +"3:"
> + "exit;"
> + :
> + : __imm(bpf_ktime_get_ns)
> + : __clobber_all);
> +}
> +
> char _license[] SEC("license") = "GPL";
> --
> 2.43.0
>
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