Subject: [PATCH] bpf: fix misaligned access for BPF_PROG_TYPE_PERF_EVENT program type on x86_32 platform

From: Wang YanQing <[email-masked]>
Date: Thu, 26 Apr 2018 17:57:49 +0800

All the testcases for BPF_PROG_TYPE_PERF_EVENT program type in
test_verifier(kselftest) report below errors on x86_32:
"
172/p unpriv: spill/fill of different pointers ldx FAIL
Unexpected error message!
0: (bf) r6 = r10
1: (07) r6 += -8
2: (15) if r1 == 0x0 goto pc+3
R1=ctx(id=0,off=0,imm=0) R6=fp-8,call_-1 R10=fp0,call_-1
3: (bf) r2 = r10
4: (07) r2 += -76
5: (7b) *(u64 *)(r6 +0) = r2
6: (55) if r1 != 0x0 goto pc+1
R1=ctx(id=0,off=0,imm=0) R2=fp-76,call_-1 R6=fp-8,call_-1 R10=fp0,call_-1 fp-8=fp
7: (7b) *(u64 *)(r6 +0) = r1
8: (79) r1 = *(u64 *)(r6 +0)
9: (79) r1 = *(u64 *)(r1 +68)
invalid bpf_context access off=68 size=8

378/p check bpf_perf_event_data->sample_period byte load permitted FAIL
Failed to load prog 'Permission denied'!
0: (b7) r0 = 0
1: (71) r0 = *(u8 *)(r1 +68)
invalid bpf_context access off=68 size=1

379/p check bpf_perf_event_data->sample_period half load permitted FAIL
Failed to load prog 'Permission denied'!
0: (b7) r0 = 0
1: (69) r0 = *(u16 *)(r1 +68)
invalid bpf_context access off=68 size=2

380/p check bpf_perf_event_data->sample_period word load permitted FAIL
Failed to load prog 'Permission denied'!
0: (b7) r0 = 0
1: (61) r0 = *(u32 *)(r1 +68)
invalid bpf_context access off=68 size=4

381/p check bpf_perf_event_data->sample_period dword load permitted FAIL
Failed to load prog 'Permission denied'!
0: (b7) r0 = 0
1: (79) r0 = *(u64 *)(r1 +68)
invalid bpf_context access off=68 size=8
"

This patch fix it, the fix isn't only necessary for x86_32, it will fix the
same problem for other platforms too, if their size of bpf_user_pt_regs_t
can't divide exactly into 8.

Signed-off-by: Wang YanQing <[email-masked]>
---
 Hi all!
 After mainline accept this patch, then we need to submit a sync patch
 to update the tools/include/uapi/linux/bpf_perf_event.h.

 Thanks.

 include/uapi/linux/bpf_perf_event.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf_perf_event.h b/include/uapi/linux/bpf_perf_event.h
index eb1b9d2..ff4c092 100644
--- a/include/uapi/linux/bpf_perf_event.h
+++ b/include/uapi/linux/bpf_perf_event.h
@@ -12,7 +12,7 @@
 
 struct bpf_perf_event_data {
 	bpf_user_pt_regs_t regs;
-	__u64 sample_period;
+	__u64 sample_period __attribute__((aligned(8)));
 	__u64 addr;
 };
 
-- 
1.8.5.6.2.g3d8a54e.dirty