selftests/bpf: Tests for is_scalar_branch_taken tnum logic

This patch adds tests for the new jeq and jne logic in
is_scalar_branch_taken. The following shows the first test failing
before the previous patch is applied. Once the previous patch is
applied, the verifier can use the tnum values to deduce that instruction
7 is dead code.

  0: call bpf_get_prandom_u32#7  ; R0_w=scalar()
  1: w0 = w0                     ; R0_w=scalar(smin=0,smax=umax=0xffffffff,var_off=(0x0; 0xffffffff))
  2: r0 >>= 30                   ; R0_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=3,var_off=(0x0; 0x3))
  3: r0 <<= 30                   ; R0_w=scalar(smin=0,smax=umax=umax32=0xc0000000,smax32=0x40000000,var_off=(0x0; 0xc0000000))
  4: r1 = r0                     ; R0_w=scalar(id=1,smin=0,smax=umax=umax32=0xc0000000,smax32=0x40000000,var_off=(0x0; 0xc0000000)) R1_w=scalar(id=1,smin=0,smax=umax=umax32=0xc0000000,smax32=0x40000000,var_off=(0x0; 0xc0000000))
  5: r1 += 1024                  ; R1_w=scalar(smin=umin=umin32=1024,smax=umax=umax32=0xc0000400,smin32=0x80000400,smax32=0x40000400,var_off=(0x400; 0xc0000000))
  6: if r1 != r0 goto pc+1       ; R0_w=scalar(id=1,smin=umin=umin32=1024,smax=umax=umax32=0xc0000000,smin32=0x80000400,smax32=0x40000000,var_off=(0x400; 0xc0000000)) R1_w=scalar(smin=umin=umin32=1024,smax=umax=umax32=0xc0000000,smin32=0x80000400,smax32=0x40000400,var_off=(0x400; 0xc0000000))
  7: r10 = 0
  frame pointer is read only

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/550004f935e2553bdb2fb1f09cbde7d0452112d0.1755694148.git.paul.chaignon@gmail.com

diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
index 87a2c60d86e6ee0e9b23b7dbc7e410d8cd893b8e..fbccc20555f48d2788f4bbcb3c591dfb46ccb49d 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
@@ -1668,4 +1668,45 @@ l0_%=:   r0 = 0;                         \
        : __clobber_all);
 }
 
+SEC("socket")
+__description("dead jne branch due to disagreeing tnums")
+__success __log_level(2)
+__naked void jne_disagreeing_tnums(void *ctx)
+{
+       asm volatile("                  \
+       call %[bpf_get_prandom_u32];    \
+       w0 = w0;                        \
+       r0 >>= 30;                      \
+       r0 <<= 30;                      \
+       r1 = r0;                        \
+       r1 += 1024;                     \
+       if r1 != r0 goto +1;            \
+       r10 = 0;                        \
+       exit;                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
+SEC("socket")
+__description("dead jeq branch due to disagreeing tnums")
+__success __log_level(2)
+__naked void jeq_disagreeing_tnums(void *ctx)
+{
+       asm volatile("                  \
+       call %[bpf_get_prandom_u32];    \
+       w0 = w0;                        \
+       r0 >>= 30;                      \
+       r0 <<= 30;                      \
+       r1 = r0;                        \
+       r1 += 1024;                     \
+       if r1 == r0 goto +1;            \
+       exit;                           \
+       r10 = 0;                        \
+       exit;                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";