selftests/bpf: Add test cases to assert proper ID tracking on spill

The previous commit fixed a verifier bypass by ensuring that ID is not
preserved on narrowing spills. Add the test cases to check the
problematic patterns.

Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20230607123951.558971-3-maxtram95@gmail.com

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index 136e5530b72cf6663202cdf1c896b0b0baeb6756..6115520154e330929e02004a6a9d64b37e51a45f 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -371,4 +371,83 @@ __naked void and_then_at_fp_8(void)
 "      ::: __clobber_all);
 }
 
+SEC("xdp")
+__description("32-bit spill of 64-bit reg should clear ID")
+__failure __msg("math between ctx pointer and 4294967295 is not allowed")
+__naked void spill_32bit_of_64bit_fail(void)
+{
+       asm volatile ("                                 \
+       r6 = r1;                                        \
+       /* Roll one bit to force the verifier to track both branches. */\
+       call %[bpf_get_prandom_u32];                    \
+       r0 &= 0x8;                                      \
+       /* Put a large number into r1. */               \
+       r1 = 0xffffffff;                                \
+       r1 <<= 32;                                      \
+       r1 += r0;                                       \
+       /* Assign an ID to r1. */                       \
+       r2 = r1;                                        \
+       /* 32-bit spill r1 to stack - should clear the ID! */\
+       *(u32*)(r10 - 8) = r1;                          \
+       /* 32-bit fill r2 from stack. */                \
+       r2 = *(u32*)(r10 - 8);                          \
+       /* Compare r2 with another register to trigger find_equal_scalars.\
+        * Having one random bit is important here, otherwise the verifier cuts\
+        * the corners. If the ID was mistakenly preserved on spill, this would\
+        * cause the verifier to think that r1 is also equal to zero in one of\
+        * the branches, and equal to eight on the other branch.\
+        */                                             \
+       r3 = 0;                                         \
+       if r2 != r3 goto l0_%=;                         \
+l0_%=: r1 >>= 32;                                      \
+       /* At this point, if the verifier thinks that r1 is 0, an out-of-bounds\
+        * read will happen, because it actually contains 0xffffffff.\
+        */                                             \
+       r6 += r1;                                       \
+       r0 = *(u32*)(r6 + 0);                           \
+       exit;                                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
+SEC("xdp")
+__description("16-bit spill of 32-bit reg should clear ID")
+__failure __msg("dereference of modified ctx ptr R6 off=65535 disallowed")
+__naked void spill_16bit_of_32bit_fail(void)
+{
+       asm volatile ("                                 \
+       r6 = r1;                                        \
+       /* Roll one bit to force the verifier to track both branches. */\
+       call %[bpf_get_prandom_u32];                    \
+       r0 &= 0x8;                                      \
+       /* Put a large number into r1. */               \
+       w1 = 0xffff0000;                                \
+       r1 += r0;                                       \
+       /* Assign an ID to r1. */                       \
+       r2 = r1;                                        \
+       /* 16-bit spill r1 to stack - should clear the ID! */\
+       *(u16*)(r10 - 8) = r1;                          \
+       /* 16-bit fill r2 from stack. */                \
+       r2 = *(u16*)(r10 - 8);                          \
+       /* Compare r2 with another register to trigger find_equal_scalars.\
+        * Having one random bit is important here, otherwise the verifier cuts\
+        * the corners. If the ID was mistakenly preserved on spill, this would\
+        * cause the verifier to think that r1 is also equal to zero in one of\
+        * the branches, and equal to eight on the other branch.\
+        */                                             \
+       r3 = 0;                                         \
+       if r2 != r3 goto l0_%=;                         \
+l0_%=: r1 >>= 16;                                      \
+       /* At this point, if the verifier thinks that r1 is 0, an out-of-bounds\
+        * read will happen, because it actually contains 0xffff.\
+        */                                             \
+       r6 += r1;                                       \
+       r0 = *(u32*)(r6 + 0);                           \
+       exit;                                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";