Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
The assembly function "reg_not_equal()" that we add is exactly converted
from the following case:
u32 a = bpf_get_prandom_u32();
u64 b = 0;
a %= 8;
/* the "a > 0" here will be optimized to "a != 0" */
if (a > 0) {
/* now the range of a should be [1, 7] */
bpf_skb_store_bytes(skb, 0, &b, a, 0);
}
Signed-off-by: Menglong Dong <[email protected]>
---
.../selftests/bpf/progs/verifier_bounds.c | 27 +++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
index ec430b71730b..3fe2ce2b3f21 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
@@ -1075,4 +1075,31 @@ l0_%=: r0 = 0; \
: __clobber_all);
}
+SEC("tc")
+__description("bounds check with JMP_NE for reg edge")
+__success __retval(0)
+__naked void reg_not_equal(void)
+{
+ asm volatile (" \
+ r6 = r1; \
+ r1 = 0; \
+ *(u64*)(r10 - 8) = r1; \
+ call %[bpf_get_prandom_u32]; \
+ r4 = r0; \
+ r4 &= 7; \
+ if r4 == 0 goto l0_%=; \
+ r1 = r6; \
+ r2 = 0; \
+ r3 = r10; \
+ r3 += -8; \
+ r5 = 0; \
+ call %[bpf_skb_store_bytes]; \
+l0_%=: r0 = 0; \
+ exit; \
+" :
+ : __imm(bpf_get_prandom_u32),
+ __imm(bpf_skb_store_bytes)
+ : __clobber_all);
+}
+
char _license[] SEC("license") = "GPL";
--
2.39.2
On Sun, Dec 17, 2023 at 5:18 AM Menglong Dong <[email protected]> wrote:
>
> Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
> The assembly function "reg_not_equal()" that we add is exactly converted
> from the following case:
>
> u32 a = bpf_get_prandom_u32();
> u64 b = 0;
>
> a %= 8;
> /* the "a > 0" here will be optimized to "a != 0" */
> if (a > 0) {
> /* now the range of a should be [1, 7] */
> bpf_skb_store_bytes(skb, 0, &b, a, 0);
> }
>
> Signed-off-by: Menglong Dong <[email protected]>
> ---
> .../selftests/bpf/progs/verifier_bounds.c | 27 +++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
LGTM, but please add a comment that we rely on bpf_skb_store_byte's
4th argument being defined as ARG_CONST_SIZE, so zero is not allowed.
And that r4 == 0 check is providing us this exclusion of zero from
initial [0, 7] range.
> diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> index ec430b71730b..3fe2ce2b3f21 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> @@ -1075,4 +1075,31 @@ l0_%=: r0 = 0; \
> : __clobber_all);
> }
>
> +SEC("tc")
> +__description("bounds check with JMP_NE for reg edge")
> +__success __retval(0)
> +__naked void reg_not_equal(void)
technically, you are testing `r4 == 0` :) so maybe call the test
reg_equal_const or something. And then add similar test where you
actually have `r4 != 0`, called req_no_equal_const?
> +{
> + asm volatile (" \
> + r6 = r1; \
> + r1 = 0; \
> + *(u64*)(r10 - 8) = r1; \
> + call %[bpf_get_prandom_u32]; \
> + r4 = r0; \
> + r4 &= 7; \
> + if r4 == 0 goto l0_%=; \
> + r1 = r6; \
> + r2 = 0; \
> + r3 = r10; \
> + r3 += -8; \
> + r5 = 0; \
> + call %[bpf_skb_store_bytes]; \
> +l0_%=: r0 = 0; \
> + exit; \
> +" :
> + : __imm(bpf_get_prandom_u32),
> + __imm(bpf_skb_store_bytes)
> + : __clobber_all);
> +}
> +
> char _license[] SEC("license") = "GPL";
> --
> 2.39.2
>
On Tue, Dec 19, 2023 at 2:03 AM Andrii Nakryiko
<[email protected]> wrote:
>
> On Sun, Dec 17, 2023 at 5:18 AM Menglong Dong <[email protected]> wrote:
> >
> > Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
> > The assembly function "reg_not_equal()" that we add is exactly converted
> > from the following case:
> >
> > u32 a = bpf_get_prandom_u32();
> > u64 b = 0;
> >
> > a %= 8;
> > /* the "a > 0" here will be optimized to "a != 0" */
> > if (a > 0) {
> > /* now the range of a should be [1, 7] */
> > bpf_skb_store_bytes(skb, 0, &b, a, 0);
> > }
> >
> > Signed-off-by: Menglong Dong <[email protected]>
> > ---
> > .../selftests/bpf/progs/verifier_bounds.c | 27 +++++++++++++++++++
> > 1 file changed, 27 insertions(+)
> >
>
> LGTM, but please add a comment that we rely on bpf_skb_store_byte's
> 4th argument being defined as ARG_CONST_SIZE, so zero is not allowed.
> And that r4 == 0 check is providing us this exclusion of zero from
> initial [0, 7] range.
>
Okay, sounds great! BTW, should I add such a comment to the
commit log or to the assembly function?
>
> > diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > index ec430b71730b..3fe2ce2b3f21 100644
> > --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > @@ -1075,4 +1075,31 @@ l0_%=: r0 = 0; \
> > : __clobber_all);
> > }
> >
> > +SEC("tc")
> > +__description("bounds check with JMP_NE for reg edge")
> > +__success __retval(0)
> > +__naked void reg_not_equal(void)
>
> technically, you are testing `r4 == 0` :) so maybe call the test
> reg_equal_const or something. And then add similar test where you
> actually have `r4 != 0`, called req_no_equal_const?
>
Yeah, that makes sense. I'll add such a test in the next version.
Thanks!
Menglong Dong
> > +{
> > + asm volatile (" \
> > + r6 = r1; \
> > + r1 = 0; \
> > + *(u64*)(r10 - 8) = r1; \
> > + call %[bpf_get_prandom_u32]; \
> > + r4 = r0; \
> > + r4 &= 7; \
> > + if r4 == 0 goto l0_%=; \
> > + r1 = r6; \
> > + r2 = 0; \
> > + r3 = r10; \
> > + r3 += -8; \
> > + r5 = 0; \
> > + call %[bpf_skb_store_bytes]; \
> > +l0_%=: r0 = 0; \
> > + exit; \
> > +" :
> > + : __imm(bpf_get_prandom_u32),
> > + __imm(bpf_skb_store_bytes)
> > + : __clobber_all);
> > +}
> > +
> > char _license[] SEC("license") = "GPL";
> > --
> > 2.39.2
> >
On Mon, Dec 18, 2023 at 6:27 PM Menglong Dong <[email protected]> wrote:
>
> On Tue, Dec 19, 2023 at 2:03 AM Andrii Nakryiko
> <[email protected]> wrote:
> >
> > On Sun, Dec 17, 2023 at 5:18 AM Menglong Dong <[email protected]> wrote:
> > >
> > > Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
> > > The assembly function "reg_not_equal()" that we add is exactly converted
> > > from the following case:
> > >
> > > u32 a = bpf_get_prandom_u32();
> > > u64 b = 0;
> > >
> > > a %= 8;
> > > /* the "a > 0" here will be optimized to "a != 0" */
> > > if (a > 0) {
> > > /* now the range of a should be [1, 7] */
> > > bpf_skb_store_bytes(skb, 0, &b, a, 0);
> > > }
> > >
> > > Signed-off-by: Menglong Dong <[email protected]>
> > > ---
> > > .../selftests/bpf/progs/verifier_bounds.c | 27 +++++++++++++++++++
> > > 1 file changed, 27 insertions(+)
> > >
> >
> > LGTM, but please add a comment that we rely on bpf_skb_store_byte's
> > 4th argument being defined as ARG_CONST_SIZE, so zero is not allowed.
> > And that r4 == 0 check is providing us this exclusion of zero from
> > initial [0, 7] range.
> >
>
> Okay, sounds great! BTW, should I add such a comment to the
> commit log or to the assembly function?
>
I'd leave it in the code, next to the function itself
> >
> > > diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > > index ec430b71730b..3fe2ce2b3f21 100644
> > > --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > > +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > > @@ -1075,4 +1075,31 @@ l0_%=: r0 = 0; \
> > > : __clobber_all);
> > > }
> > >
> > > +SEC("tc")
> > > +__description("bounds check with JMP_NE for reg edge")
> > > +__success __retval(0)
> > > +__naked void reg_not_equal(void)
> >
> > technically, you are testing `r4 == 0` :) so maybe call the test
> > reg_equal_const or something. And then add similar test where you
> > actually have `r4 != 0`, called req_no_equal_const?
> >
>
> Yeah, that makes sense. I'll add such a test in the next version.
>
> Thanks!
> Menglong Dong
>
> > > +{
> > > + asm volatile (" \
> > > + r6 = r1; \
> > > + r1 = 0; \
> > > + *(u64*)(r10 - 8) = r1; \
> > > + call %[bpf_get_prandom_u32]; \
> > > + r4 = r0; \
> > > + r4 &= 7; \
> > > + if r4 == 0 goto l0_%=; \
> > > + r1 = r6; \
> > > + r2 = 0; \
> > > + r3 = r10; \
> > > + r3 += -8; \
> > > + r5 = 0; \
> > > + call %[bpf_skb_store_bytes]; \
> > > +l0_%=: r0 = 0; \
> > > + exit; \
> > > +" :
> > > + : __imm(bpf_get_prandom_u32),
> > > + __imm(bpf_skb_store_bytes)
> > > + : __clobber_all);
> > > +}
> > > +
> > > char _license[] SEC("license") = "GPL";
> > > --
> > > 2.39.2
> > >