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Date: Fri, 22 Dec 2017 19:12:35 +0100
From: Jann Horn <jannh@...gle.com>
To: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: selftest for late caller stack size increase
This checks that it is not possible to bypass the total stack size check in
update_stack_depth() by calling a function that uses a large amount of
stack memory *before* using a large amount of stack memory in the caller.
Currently, the first added testcase causes a rejection as expected, but
the second testcase is (AFAICS incorrectly) accepted:
[...]
#483/p calls: stack overflow using two frames (post-call access) FAIL
Unexpected success to load!
0: (85) call pc+2
caller:
R10=fp0,call_-1
callee:
frame1: R1=ctx(id=0,off=0,imm=0) R10=fp0,call_0
3: (72) *(u8 *)(r10 -300) = 0
4: (b7) r0 = 0
5: (95) exit
returning from callee:
frame1: R0_w=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0,call_0
to caller at 1:
R0_w=inv0 R10=fp0,call_-1
from 5 to 1: R0=inv0 R10=fp0,call_-1
1: (72) *(u8 *)(r10 -300) = 0
2: (95) exit
processed 6 insns, stack depth 300+300
[...]
Summary: 704 PASSED, 1 FAILED
AFAICS the JIT-generated code for the second testcase shows that this
really causes the stack pointer to be decremented by 300+300:
first function:
00000000 55 push rbp
00000001 4889E5 mov rbp,rsp
00000004 4881EC58010000 sub rsp,0x158
0000000B 4883ED28 sub rbp,byte +0x28
[...]
00000025 E89AB3AFE5 call 0xffffffffe5afb3c4
0000002A C685D4FEFFFF00 mov byte [rbp-0x12c],0x0
[...]
00000041 4883C528 add rbp,byte +0x28
00000045 C9 leave
00000046 C3 ret
second function:
00000000 55 push rbp
00000001 4889E5 mov rbp,rsp
00000004 4881EC58010000 sub rsp,0x158
0000000B 4883ED28 sub rbp,byte +0x28
[...]
00000025 C685D4FEFFFF00 mov byte [rbp-0x12c],0x0
[...]
0000003E 4883C528 add rbp,byte +0x28
00000042 C9 leave
00000043 C3 ret
Signed-off-by: Jann Horn <jannh@...gle.com>
---
tools/testing/selftests/bpf/test_verifier.c | 34 +++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 3bacff0d6f91..71fb0be81b78 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -8729,6 +8729,40 @@ static struct bpf_test tests[] = {
.prog_type = BPF_PROG_TYPE_XDP,
.result = ACCEPT,
},
+ {
+ "calls: stack overflow using two frames (pre-call access)",
+ .insns = {
+ /* prog 1 */
+ BPF_ST_MEM(BPF_B, BPF_REG_10, -300, 0),
+ BPF_RAW_INSN(BPF_JMP|BPF_CALL, 0, 1, 0, 1),
+ BPF_EXIT_INSN(),
+
+ /* prog 2 */
+ BPF_ST_MEM(BPF_B, BPF_REG_10, -300, 0),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .prog_type = BPF_PROG_TYPE_XDP,
+ .errstr = "combined stack size",
+ .result = REJECT,
+ },
+ {
+ "calls: stack overflow using two frames (post-call access)",
+ .insns = {
+ /* prog 1 */
+ BPF_RAW_INSN(BPF_JMP|BPF_CALL, 0, 1, 0, 2),
+ BPF_ST_MEM(BPF_B, BPF_REG_10, -300, 0),
+ BPF_EXIT_INSN(),
+
+ /* prog 2 */
+ BPF_ST_MEM(BPF_B, BPF_REG_10, -300, 0),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .prog_type = BPF_PROG_TYPE_XDP,
+ .errstr = "combined stack size",
+ .result = REJECT,
+ },
{
"calls: spill into caller stack frame",
.insns = {
--
2.15.1.620.gb9897f4670-goog
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