* [PATCH] bpf: fix probe read error in ___bpf_prog_run()
@ 2022-05-23 7:37 menglong8.dong
2022-05-23 20:25 ` Daniel Borkmann
0 siblings, 1 reply; 2+ messages in thread
From: menglong8.dong @ 2022-05-23 7:37 UTC (permalink / raw)
To: ast
Cc: daniel, andrii, kafai, songliubraving, yhs, john.fastabend,
kpsingh, netdev, bpf, linux-kernel, Menglong Dong, Jiang Biao,
Hao Peng
From: Menglong Dong <imagedong@tencent.com>
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@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
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)
#undef LDX_PROBE
#define ATOMIC_ALU_OP(BOP, KOP) \
--
2.36.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] bpf: fix probe read error in ___bpf_prog_run()
2022-05-23 7:37 [PATCH] bpf: fix probe read error in ___bpf_prog_run() menglong8.dong
@ 2022-05-23 20:25 ` Daniel Borkmann
0 siblings, 0 replies; 2+ messages in thread
From: Daniel Borkmann @ 2022-05-23 20:25 UTC (permalink / raw)
To: menglong8.dong, ast
Cc: andrii, kafai, songliubraving, yhs, john.fastabend, kpsingh,
netdev, bpf, linux-kernel, Menglong Dong, Jiang Biao, Hao Peng
On 5/23/22 9:37 AM, menglong8.dong@gmail.com wrote:
> From: Menglong Dong <imagedong@tencent.com>
>
> 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@tencent.com>
> Reviewed-by: Hao Peng <flyingpeng@tencent.com>
> Signed-off-by: Menglong Dong <imagedong@tencent.com>
> ---
> 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
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2022-05-23 7:37 [PATCH] bpf: fix probe read error in ___bpf_prog_run() menglong8.dong
2022-05-23 20:25 ` Daniel Borkmann
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