This is based on the gadget from the description of commit 9183671af6db ("bpf: Fix leakage under speculation on mispredicted branches").
Signed-off-by: Luis Gerhorst luis.gerhorst@fau.de --- .../selftests/bpf/progs/verifier_unpriv.c | 57 +++++++++++++++++++ 1 file changed, 57 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/testing/selftests/bpf/progs/verifier_unpriv.c index c42c3839b30c..43236b93ebb5 100644 --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c @@ -729,4 +729,61 @@ l0_%=: r0 = 0; \ " ::: __clobber_all); }
+SEC("socket") +__description("unpriv: Spectre v1 path-based type confusion of scalar as stack-ptr") +__success __success_unpriv __retval(0) +#ifdef SPEC_V1 +__xlated_unpriv("if r0 != 0x1 goto pc+2") +/* This nospec prevents the exploit because it forces the mispredicted (not + * taken) `if r0 != 0x0 goto l0_%=` to resolve before using r6 as a pointer. + * This causes the CPU to realize that `r6 = r9` should have never executed. It + * ensures that r6 always contains a readable stack slot ptr when the insn after + * the nospec executes. + */ +__xlated_unpriv("nospec") +__xlated_unpriv("r9 = *(u8 *)(r6 +0)") +#endif +__naked void unpriv_spec_v1_type_confusion(void) +{ + asm volatile (" \ + r1 = 0; \ + *(u64*)(r10 - 8) = r1; \ + r2 = r10; \ + r2 += -8; \ + r1 = %[map_hash_8b] ll; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto l2_%=; \ + /* r0: pointer to a map array entry */ \ + r2 = r10; \ + r2 += -8; \ + r1 = %[map_hash_8b] ll; \ + /* r1, r2: prepared call args */ \ + r6 = r10; \ + r6 += -8; \ + /* r6: pointer to readable stack slot */ \ + r9 = 0xffffc900; \ + r9 <<= 32; \ + /* r9: scalar controlled by attacker */ \ + r0 = *(u64 *)(r0 + 0); /* cache miss */ \ + if r0 != 0x0 goto l0_%=; \ + r6 = r9; \ +l0_%=: if r0 != 0x1 goto l1_%=; \ + r9 = *(u8 *)(r6 + 0); \ +l1_%=: /* leak r9 */ \ + r9 &= 1; \ + r9 <<= 9; \ + *(u64*)(r10 - 8) = r9; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto l2_%=; \ + /* leak secret into is_cached(map[0|512]): */ \ + r0 = *(u64 *)(r0 + 0); \ +l2_%=: \ + r0 = 0; \ + exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_hash_8b) + : __clobber_all); +} + char _license[] SEC("license") = "GPL";