Commit f57ade27 authored by Maxim Mikityanskiy's avatar Maxim Mikityanskiy Committed by Daniel Borkmann
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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: default avatarMaxim Mikityanskiy <maxim@isovalent.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20230607123951.558971-3-maxtram95@gmail.com
parent 713274f1

tools/testing/selftests/bpf/progs/verifier_spill_fill.c

+79 −0
Original line number Diff line number Diff line
@@ -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";