selftests/bpf: Add test cases for narrowing fill

The previous commit allowed to preserve boundaries and track IDs of
scalars on narrowing fills. Add test cases for that pattern.

Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240127175237.526726-5-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 3e5d063ea7e8239ebf08c1a686607576517e3f77..7f3b1319bd99143ac8d0f91a901c5b67c8d16fe5 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -979,4 +979,115 @@ l0_%=:    r0 = 0;                                         \
        : __clobber_all);
 }
 
+SEC("xdp")
+__description("32-bit fill after 64-bit spill")
+__success __retval(0)
+__naked void fill_32bit_after_spill_64bit(void)
+{
+       asm volatile("                                  \
+       /* Randomize the upper 32 bits. */              \
+       call %[bpf_get_prandom_u32];                    \
+       r0 <<= 32;                                      \
+       /* 64-bit spill r0 to stack. */                 \
+       *(u64*)(r10 - 8) = r0;                          \
+       /* 32-bit fill r0 from stack. */                \
+       "
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+       "r0 = *(u32*)(r10 - 8);"
+#else
+       "r0 = *(u32*)(r10 - 4);"
+#endif
+       "                                               \
+       /* Boundary check on r0 with predetermined result. */\
+       if r0 == 0 goto l0_%=;                          \
+       /* Dead branch: the verifier should prune it. Do an invalid memory\
+        * access if the verifier follows it.           \
+        */                                             \
+       r0 = *(u64*)(r9 + 0);                           \
+l0_%=: exit;                                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
+SEC("xdp")
+__description("32-bit fill after 64-bit spill of 32-bit value should preserve ID")
+__success __retval(0)
+__naked void fill_32bit_after_spill_64bit_preserve_id(void)
+{
+       asm volatile ("                                 \
+       /* Randomize the lower 32 bits. */              \
+       call %[bpf_get_prandom_u32];                    \
+       w0 &= 0xffffffff;                               \
+       /* 64-bit spill r0 to stack - should assign an ID. */\
+       *(u64*)(r10 - 8) = r0;                          \
+       /* 32-bit fill r1 from stack - should preserve the ID. */\
+       "
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+       "r1 = *(u32*)(r10 - 8);"
+#else
+       "r1 = *(u32*)(r10 - 4);"
+#endif
+       "                                               \
+       /* Compare r1 with another register to trigger find_equal_scalars. */\
+       r2 = 0;                                         \
+       if r1 != r2 goto l0_%=;                         \
+       /* The result of this comparison is predefined. */\
+       if r0 == r2 goto l0_%=;                         \
+       /* Dead branch: the verifier should prune it. Do an invalid memory\
+        * access if the verifier follows it.           \
+        */                                             \
+       r0 = *(u64*)(r9 + 0);                           \
+       exit;                                           \
+l0_%=: r0 = 0;                                         \
+       exit;                                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
+SEC("xdp")
+__description("32-bit fill after 64-bit spill should clear ID")
+__failure __msg("math between ctx pointer and 4294967295 is not allowed")
+__naked void fill_32bit_after_spill_64bit_clear_id(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;                                       \
+       /* 64-bit spill r1 to stack - should assign an ID. */\
+       *(u64*)(r10 - 8) = r1;                          \
+       /* 32-bit fill r2 from stack - should clear the ID. */\
+       "
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+       "r2 = *(u32*)(r10 - 8);"
+#else
+       "r2 = *(u32*)(r10 - 4);"
+#endif
+       "                                               \
+       /* 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 fill, 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;                                      \
+       /* The verifier shouldn't propagate r2's range to r1, so it should\
+        * still remember r1 = 0xffffffff and reject the below.\
+        */                                             \
+       r6 += r1;                                       \
+       r0 = *(u32*)(r6 + 0);                           \
+       exit;                                           \
+"      :
+       : __imm(bpf_get_prandom_u32)
+       : __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";