Re: [PATCH] bpf: fix probe read error in ___bpf_prog_run()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 5/23/22 9:37 AM, menglong8.dong@xxxxxxxxx wrote:
From: Menglong Dong <imagedong@xxxxxxxxxxx>

I think there is something wrong with BPF_PROBE_MEM in ___bpf_prog_run()
in big-endian machine. Let's make a test and see what will happen if we
want to load a 'u16' with BPF_PROBE_MEM.

Let's make the src value '0x0001', the value of dest register will become
0x0001000000000000, as the value will be loaded to the first 2 byte of
DST with following code:

   bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off));

Obviously, the value in DST is not correct. In fact, we can compare
BPF_PROBE_MEM with LDX_MEM_H:

   DST = *(SIZE *)(unsigned long) (SRC + insn->off);

If the memory load is done by LDX_MEM_H, the value in DST will be 0x1 now.

And I think this error results in the test case 'test_bpf_sk_storage_map'
failing:

   test_bpf_sk_storage_map:PASS:bpf_iter_bpf_sk_storage_map__open_and_load 0 nsec
   test_bpf_sk_storage_map:PASS:socket 0 nsec
   test_bpf_sk_storage_map:PASS:map_update 0 nsec
   test_bpf_sk_storage_map:PASS:socket 0 nsec
   test_bpf_sk_storage_map:PASS:map_update 0 nsec
   test_bpf_sk_storage_map:PASS:socket 0 nsec
   test_bpf_sk_storage_map:PASS:map_update 0 nsec
   test_bpf_sk_storage_map:PASS:attach_iter 0 nsec
   test_bpf_sk_storage_map:PASS:create_iter 0 nsec
   test_bpf_sk_storage_map:PASS:read 0 nsec
   test_bpf_sk_storage_map:FAIL:ipv6_sk_count got 0 expected 3
   $10/26 bpf_iter/bpf_sk_storage_map:FAIL

The code of the test case is simply, it will load sk->sk_family to the
register with BPF_PROBE_MEM and check if it is AF_INET6. With this patch,
now the test case 'bpf_iter' can pass:

   $10  bpf_iter:OK

Reviewed-by: Jiang Biao <benbjiang@xxxxxxxxxxx>
Reviewed-by: Hao Peng <flyingpeng@xxxxxxxxxxx>
Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
---
  kernel/bpf/core.c | 11 ++++++-----
  1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 13e9dbeeedf3..09e3f374739a 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1945,14 +1945,15 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
  	LDST(W,  u32)
  	LDST(DW, u64)
  #undef LDST
-#define LDX_PROBE(SIZEOP, SIZE)							\
+#define LDX_PROBE(SIZEOP, SIZE, TYPE)						\
  	LDX_PROBE_MEM_##SIZEOP:							\
  		bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off));	\
+		DST = *((TYPE *)&DST);						\
  		CONT;
-	LDX_PROBE(B,  1)
-	LDX_PROBE(H,  2)
-	LDX_PROBE(W,  4)
-	LDX_PROBE(DW, 8)
+	LDX_PROBE(B,  1, u8)
+	LDX_PROBE(H,  2, u16)
+	LDX_PROBE(W,  4, u32)
+	LDX_PROBE(DW, 8, u64)

Completely uncompiled, but maybe just fold it into LDST instead:

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9cc91f0f3115..fc5c29243739 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1948,6 +1948,11 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
                CONT;                                                   \
        LDX_MEM_##SIZEOP:                                               \
                DST = *(SIZE *)(unsigned long) (SRC + insn->off);       \
+               CONT;                                                   \
+       LDX_PROBE_MEM_##SIZEOP:                                         \
+               bpf_probe_read_kernel(&DST, sizeof(SIZE),               \
+                                     (const void *)(long)(SRC + insn->off)); \
+               DST = *((SIZE *)&DST);                                  \
                CONT;

        LDST(B,   u8)
@@ -1955,15 +1960,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
        LDST(W,  u32)
        LDST(DW, u64)
 #undef LDST
-#define LDX_PROBE(SIZEOP, SIZE)                                                        \
-       LDX_PROBE_MEM_##SIZEOP:                                                 \
-               bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off));      \
-               CONT;
-       LDX_PROBE(B,  1)
-       LDX_PROBE(H,  2)
-       LDX_PROBE(W,  4)
-       LDX_PROBE(DW, 8)
-#undef LDX_PROBE

Thanks,
Daniel



[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux