On Tue, Jun 24, 2025 at 3:45 PM Eduard Zingerman wrote:
>
> On Mon, 2025-06-23 at 00:03 -0400, Harishankar Vishwanathan wrote:
> > The previous commit improves the precision in scalar(32)_min_max_add,
> > and scalar(32)_min_max_sub. The improvement in precision occurs in cases
> > when all outcomes overflow or underflow, respectively.
> >
> > This commit adds selftests that exercise those cases.
> >
> > This commit also adds selftests for cases where the output register
> > state bounds for u(32)_min/u(32)_max are conservatively set to unbounded
> > (when there is partial overflow or underflow).
> >
> > Signed-off-by: Harishankar Vishwanathan
> > Co-developed-by: Matan Shachnai
> > Signed-off-by: Matan Shachnai
> > Suggested-by: Eduard Zingerman
> > ---
>
> Thank you for adding these tests. Even with "human readable" numbers
> took me 15-20 minutes to verify the numbers :)
>
> Acked-by: Eduard Zingerman
>
> > .../selftests/bpf/progs/verifier_bounds.c | 161 ++
> > 1 file changed, 161 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > index 30e16153fdf1..31986f6c609e 100644
> > --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> > @@ -1371,4 +1371,165 @@ __naked void mult_sign_ovf(void)
> > __imm(bpf_skb_store_bytes)
> > : __clobber_all);
> > }
> > +
> > +SEC("socket")
> > +__description("64-bit addition, all outcomes overflow")
> > +__success __log_level(2)
> > +__msg("5: (0f) r3 += r3 {{.*}}
> > R3_w=scalar(umin=0x4000,umax=0xfffe)")
> > +__retval(0)
> > +__naked void add64_full_overflow(void)
> > +{
> > + asm volatile (
> > + "r4 = 0;"
> > + "r4 = -r4;"
>
> Nit: there is a change in the workings that would make range
> propagation in negation instruction, a better way to get unbound
> scalar here is e.g. call to bpf_get_prandom_u32() or read from a
> constant global map.
> Depending on order in which patches would be accepted this rework
> would be either on you or on the other patch-set author.
Fixed them up like below while applying:
diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c
b/tools/testing/selftests/bpf/progs/verifier_bounds.c
index 31986f6c609e..e52a24e15b34 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
@@ -1380,15 +1380,15 @@ __retval(0)
__naked void add64_full_overflow(void)
{
asm volatile (
- "r4 = 0;"
- "r4 = -r4;"
+ "call %[bpf_get_prandom_u32];"
+ "r4 = r0;"
"r3 = 0xa000 ll;"
"r3 |= r4;"
"r3 += r3;"
"r0 = 0;"
"exit"
:
- :
+ : __imm(bpf_get_prandom_u32)
: __clobber_all);
}
@@ -1400,15 +1400,15 @@ __retval(0)
__naked void add64_partial_overflow(void)
{
asm volatile (
- "r4 = 0;"
- "r4 = -r4;"
+ "call %[bpf_get_prandom_u32];"
+ "r4 = r0;"
"r3 = 2;"
"r3 |= r4;"
"r3 += r3;"
"r0 = 0;"
"exit"
:
- :
+ : __imm(bpf_get_prandom_u32)
: __clobber_all);
}
etc
