From: Maxim Mikityanskiy <maxim@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
---
.../selftests/bpf/progs/verifier_spill_fill.c | 79 +++++++++++++++++++
1 file changed, 79 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index 136e5530b72c..6115520154e3 100644
--- 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";
--
2.40.1
