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authorDaniel Borkmann <daniel@iogearbox.net>2021-12-07 10:07:04 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-12-22 09:32:35 +0100
commitefcad725feb44d6cfcd9742b6a354002bf09c9da (patch)
tree1fdd5382991f46c3abc95c3e7ecb4386afe3c8ed /tools/testing
parent423628125a484538111c2c6d9bb1588eb086053b (diff)
bpf, selftests: Add test case for atomic fetch on spilled pointer
commit 180486b430f4e22cc00a478163d942804baae4b5 upstream. Test whether unprivileged would be able to leak the spilled pointer either by exporting the returned value from the atomic{32,64} operation or by reading and exporting the value from the stack after the atomic operation took place. Note that for unprivileged, the below atomic cmpxchg test case named "Dest pointer in r0 - succeed" is failing. The reason is that in the dst memory location (r10 -8) there is the spilled register r10: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (bf) r0 = r10 1: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (7b) *(u64 *)(r10 -8) = r0 2: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=fp 2: (b7) r1 = 0 3: R0_w=fp0 R1_w=invP0 R10=fp0 fp-8_w=fp 3: (db) r0 = atomic64_cmpxchg((u64 *)(r10 -8), r0, r1) 4: R0_w=fp0 R1_w=invP0 R10=fp0 fp-8_w=mmmmmmmm 4: (79) r1 = *(u64 *)(r0 -8) 5: R0_w=fp0 R1_w=invP(id=0) R10=fp0 fp-8_w=mmmmmmmm 5: (b7) r0 = 0 6: R0_w=invP0 R1_w=invP(id=0) R10=fp0 fp-8_w=mmmmmmmm 6: (95) exit However, allowing this case for unprivileged is a bit useless given an update with a new pointer will fail anyway: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (bf) r0 = r10 1: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (7b) *(u64 *)(r10 -8) = r0 2: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=fp 2: (db) r0 = atomic64_cmpxchg((u64 *)(r10 -8), r0, r10) R10 leaks addr into mem Acked-by: Brendan Jackman <jackmanb@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org> [only backport one test for 5.15.y - gregkh] Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'tools/testing')
-rw-r--r--tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c b/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
index 6e52dfc64415..ad17e382d06e 100644
--- a/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
+++ b/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
@@ -118,4 +118,27 @@
BPF_EXIT_INSN(),
},
.result = ACCEPT,
+ .result_unpriv = REJECT,
+ .errstr_unpriv = "leaking pointer from stack off -8",
+},
+{
+ "Dest pointer in r0 - succeed, check 2",
+ .insns = {
+ /* r0 = &val */
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_10),
+ /* val = r0; */
+ BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0, -8),
+ /* r5 = &val */
+ BPF_MOV64_REG(BPF_REG_5, BPF_REG_10),
+ /* r0 = atomic_cmpxchg(&val, r0, r5); */
+ BPF_ATOMIC_OP(BPF_DW, BPF_CMPXCHG, BPF_REG_10, BPF_REG_5, -8),
+ /* r1 = *r0 */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, -8),
+ /* exit(0); */
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ .result_unpriv = REJECT,
+ .errstr_unpriv = "R5 leaks addr into mem",
},