Commit 73a28d9d authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Andrii Nakryiko
Browse files

selftests/bpf: States pruning checks for scalar vs STACK_MISC 



Check that stacksafe() compares spilled scalars with STACK_MISC.
The following combinations are explored:
- old spill of imprecise scalar is equivalent to cur STACK_{MISC,INVALID}
  (plus error in unpriv mode);
- old spill of precise scalar is not equivalent to cur STACK_MISC;
- old STACK_MISC is equivalent to cur scalar;
- old STACK_MISC is not equivalent to cur non-scalar.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240127175237.526726-7-maxtram95@gmail.com
parent 6efbde20

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

+154 −0
Original line number Diff line number Diff line
@@ -1090,4 +1090,158 @@ l0_%=: r1 >>= 32; \ 
	: __clobber_all);

}



/* stacksafe(): check if stack spill of an imprecise scalar in old state

 * is considered equivalent to STACK_{MISC,INVALID} in cur state.

 */

SEC("socket")

__success __log_level(2)

__msg("8: (79) r1 = *(u64 *)(r10 -8)")

__msg("8: safe")

__msg("processed 11 insns")

/* STACK_INVALID should prevent verifier in unpriv mode from

 * considering states equivalent and force an error on second

 * verification path (entry - label 1 - label 2).

 */

__failure_unpriv

__msg_unpriv("8: (79) r1 = *(u64 *)(r10 -8)")

__msg_unpriv("9: (95) exit")

__msg_unpriv("8: (79) r1 = *(u64 *)(r10 -8)")

__msg_unpriv("invalid read from stack off -8+2 size 8")

__flag(BPF_F_TEST_STATE_FREQ)

__naked void old_imprecise_scalar_vs_cur_stack_misc(void)

{

	asm volatile(

	/* get a random value for branching */

	"call %[bpf_ktime_get_ns];"

	"if r0 == 0 goto 1f;"

	/* conjure scalar at fp-8 */

	"r0 = 42;"

	"*(u64*)(r10 - 8) = r0;"

	"goto 2f;"

"1:"

	/* conjure STACK_{MISC,INVALID} at fp-8 */

	"call %[bpf_ktime_get_ns];"

	"*(u16*)(r10 - 8) = r0;"

	"*(u16*)(r10 - 4) = r0;"

"2:"

	/* read fp-8, should be considered safe on second visit */

	"r1 = *(u64*)(r10 - 8);"

	"exit;"

	:

	: __imm(bpf_ktime_get_ns)

	: __clobber_all);

}



/* stacksafe(): check that stack spill of a precise scalar in old state

 * is not considered equivalent to STACK_MISC in cur state.

 */

SEC("socket")

__success __log_level(2)

/* verifier should visit 'if r1 == 0x2a ...' two times:

 * - once for path entry - label 2;

 * - once for path entry - label 1 - label 2.

 */

__msg("if r1 == 0x2a goto pc+0")

__msg("if r1 == 0x2a goto pc+0")

__msg("processed 15 insns")

__flag(BPF_F_TEST_STATE_FREQ)

__naked void old_precise_scalar_vs_cur_stack_misc(void)

{

	asm volatile(

	/* get a random value for branching */

	"call %[bpf_ktime_get_ns];"

	"if r0 == 0 goto 1f;"

	/* conjure scalar at fp-8 */

	"r0 = 42;"

	"*(u64*)(r10 - 8) = r0;"

	"goto 2f;"

"1:"

	/* conjure STACK_MISC at fp-8 */

	"call %[bpf_ktime_get_ns];"

	"*(u64*)(r10 - 8) = r0;"

	"*(u32*)(r10 - 4) = r0;"

"2:"

	/* read fp-8, should not be considered safe on second visit */

	"r1 = *(u64*)(r10 - 8);"

	/* use r1 in precise context */

	"if r1 == 42 goto +0;"

	"exit;"

	:

	: __imm(bpf_ktime_get_ns)

	: __clobber_all);

}



/* stacksafe(): check if STACK_MISC in old state is considered

 * equivalent to stack spill of a scalar in cur state.

 */

SEC("socket")

__success  __log_level(2)

__msg("8: (79) r0 = *(u64 *)(r10 -8)")

__msg("8: safe")

__msg("processed 11 insns")

__flag(BPF_F_TEST_STATE_FREQ)

__naked void old_stack_misc_vs_cur_scalar(void)

{

	asm volatile(

	/* get a random value for branching */

	"call %[bpf_ktime_get_ns];"

	"if r0 == 0 goto 1f;"

	/* conjure STACK_{MISC,INVALID} at fp-8 */

	"call %[bpf_ktime_get_ns];"

	"*(u16*)(r10 - 8) = r0;"

	"*(u16*)(r10 - 4) = r0;"

	"goto 2f;"

"1:"

	/* conjure scalar at fp-8 */

	"r0 = 42;"

	"*(u64*)(r10 - 8) = r0;"

"2:"

	/* read fp-8, should be considered safe on second visit */

	"r0 = *(u64*)(r10 - 8);"

	"exit;"

	:

	: __imm(bpf_ktime_get_ns)

	: __clobber_all);

}



/* stacksafe(): check that STACK_MISC in old state is not considered

 * equivalent to stack spill of a non-scalar in cur state.

 */

SEC("socket")

__success  __log_level(2)

/* verifier should process exit instructions twice:

 * - once for path entry - label 2;

 * - once for path entry - label 1 - label 2.

 */

__msg("r1 = *(u64 *)(r10 -8)")

__msg("exit")

__msg("r1 = *(u64 *)(r10 -8)")

__msg("exit")

__msg("processed 11 insns")

__flag(BPF_F_TEST_STATE_FREQ)

__naked void old_stack_misc_vs_cur_ctx_ptr(void)

{

	asm volatile(

	/* remember context pointer in r9 */

	"r9 = r1;"

	/* get a random value for branching */

	"call %[bpf_ktime_get_ns];"

	"if r0 == 0 goto 1f;"

	/* conjure STACK_MISC at fp-8 */

	"call %[bpf_ktime_get_ns];"

	"*(u64*)(r10 - 8) = r0;"

	"*(u32*)(r10 - 4) = r0;"

	"goto 2f;"

"1:"

	/* conjure context pointer in fp-8 */

	"*(u64*)(r10 - 8) = r9;"

"2:"

	/* read fp-8, should not be considered safe on second visit */

	"r1 = *(u64*)(r10 - 8);"

	"exit;"

	:

	: __imm(bpf_ktime_get_ns)

	: __clobber_all);

}



char _license[] SEC("license") = "GPL";