[PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch

[PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

bpf_probe_read_kernel() has a __weak definition in core.c and another
definition with an incompatible prototype in kernel/trace/bpf_trace.c,
when CONFIG_BPF_EVENTS is enabled.

Since the two are incompatible, there cannot be a shared declaration
in a header file, but the lack of a prototype causes a W=1 warning:

kernel/bpf/core.c:1638:12: error: no previous prototype for 'bpf_probe_read_kernel' [-Werror=missing-prototypes]

Change the core.c file to only reference the inner
bpf_probe_read_kernel_common() helper and provide a prototype for that.

Aside from the warning, this addresses a bug on 32-bit architectures
from incorrect argument passing with the mismatched prototype.

Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
--
v2: rewrite completely to fix the mismatch.
---
 include/linux/bpf.h      | 2 ++
 kernel/bpf/core.c        | 9 ++++++---
 kernel/trace/bpf_trace.c | 3 +--
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 36e4b2d8cca2..6a231ec61a87 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2619,6 +2619,8 @@ static inline void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr)
 }
 #endif /* CONFIG_BPF_SYSCALL */
 
+int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr);
+
 void __bpf_free_used_btfs(struct bpf_prog_aux *aux,
 			  struct btf_mod_pair *used_btfs, u32 len);
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 0926714641eb..e7f0d5f146fa 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -35,6 +35,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/nodemask.h>
 #include <linux/nospec.h>
+#include <linux/bpf.h>
 #include <linux/bpf_mem_alloc.h>
 #include <linux/memcontrol.h>
 
@@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code)
 }
 
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
-u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
+#ifndef CONFIG_BPF_EVENTS
+int bpf_probe_read_kernel_common(void * dst, u32 size, const void *unsafe_ptr)
 {
 	memset(dst, 0, size);
 	return -EFAULT;
 }
+#endif
 
 /**
  *	___bpf_prog_run - run eBPF program on a given context
@@ -1931,8 +1934,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 		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));	\
+		bpf_probe_read_kernel_common(&DST, sizeof(SIZE),	\
+			      (const void *)(long) (SRC + insn->off));	\
 		DST = *((SIZE *)&DST);					\
 		CONT;
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2bc41e6ac9fe..290fdce2ce53 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -223,8 +223,7 @@ const struct bpf_func_proto bpf_probe_read_user_str_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
-static __always_inline int
-bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
+int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
 {
 	int ret;
 
-- 
2.39.2

Re: [PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch

[Yonghong Song]

On 5/23/23 12:43 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> bpf_probe_read_kernel() has a __weak definition in core.c and another
> definition with an incompatible prototype in kernel/trace/bpf_trace.c,
> when CONFIG_BPF_EVENTS is enabled.
> 
> Since the two are incompatible, there cannot be a shared declaration
> in a header file, but the lack of a prototype causes a W=1 warning:
> 
> kernel/bpf/core.c:1638:12: error: no previous prototype for 'bpf_probe_read_kernel' [-Werror=missing-prototypes]
> 
> Change the core.c file to only reference the inner
> bpf_probe_read_kernel_common() helper and provide a prototype for that.
> 
> Aside from the warning, this addresses a bug on 32-bit architectures
> from incorrect argument passing with the mismatched prototype.

Could you explain what is this '32-bit architectures ... incorrect 
argument passing' thing?

> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> --
> v2: rewrite completely to fix the mismatch.
> ---
>   include/linux/bpf.h      | 2 ++
>   kernel/bpf/core.c        | 9 ++++++---
>   kernel/trace/bpf_trace.c | 3 +--
>   3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 36e4b2d8cca2..6a231ec61a87 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2619,6 +2619,8 @@ static inline void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr)
>   }
>   #endif /* CONFIG_BPF_SYSCALL */
>   
> +int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr);
> +
>   void __bpf_free_used_btfs(struct bpf_prog_aux *aux,
>   			  struct btf_mod_pair *used_btfs, u32 len);
>   
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 0926714641eb..e7f0d5f146fa 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -35,6 +35,7 @@
>   #include <linux/bpf_verifier.h>
>   #include <linux/nodemask.h>
>   #include <linux/nospec.h>
> +#include <linux/bpf.h>
>   #include <linux/bpf_mem_alloc.h>
>   #include <linux/memcontrol.h>
>   
> @@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code)
>   }
>   
>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
> -u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
> +#ifndef CONFIG_BPF_EVENTS
> +int bpf_probe_read_kernel_common(void * dst, u32 size, const void *unsafe_ptr)

void * dst => void *dst

>   {
>   	memset(dst, 0, size);
>   	return -EFAULT;
>   }
> +#endif
>   
>   /**
>    *	___bpf_prog_run - run eBPF program on a given context
> @@ -1931,8 +1934,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
>   		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));	\
> +		bpf_probe_read_kernel_common(&DST, sizeof(SIZE),	\
> +			      (const void *)(long) (SRC + insn->off));	\
>   		DST = *((SIZE *)&DST);					\
>   		CONT;
>   
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 2bc41e6ac9fe..290fdce2ce53 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -223,8 +223,7 @@ const struct bpf_func_proto bpf_probe_read_user_str_proto = {
>   	.arg3_type	= ARG_ANYTHING,
>   };
>   
> -static __always_inline int
> -bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
> +int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
>   {
>   	int ret;
>   

Re: [PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch

[Arnd Bergmann]

On Wed, May 24, 2023, at 05:12, Yonghong Song wrote:
> On 5/23/23 12:43 PM, Arnd Bergmann wrote:

>> Aside from the warning, this addresses a bug on 32-bit architectures
>> from incorrect argument passing with the mismatched prototype.
>
> Could you explain what is this '32-bit architectures ... incorrect 
> argument passing' thing?

I've expanded that paragraph now:

| Aside from the warning, this addresses a bug on 32-bit architectures
| from incorrect argument passing with the mismatched prototype:
| BPF_CALL_x() functions use 64-bit arguments that are passed in
| pairs of register or on the stack on 32-bit architectures, while the
| normal function uses one register per argument.

Let me know if you think I should put more details in there.

>> @@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code)
>>   }
>>   
>>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>> -u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
>> +#ifndef CONFIG_BPF_EVENTS
>> +int bpf_probe_read_kernel_common(void * dst, u32 size, const void *unsafe_ptr)
>
> void * dst => void *dst
>

Fixed now.

Thanks,

     Arnd

Re: [PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch

[Yonghong Song]

On 5/24/23 6:28 AM, Arnd Bergmann wrote:
> On Wed, May 24, 2023, at 05:12, Yonghong Song wrote:
>> On 5/23/23 12:43 PM, Arnd Bergmann wrote:
> 
>>> Aside from the warning, this addresses a bug on 32-bit architectures
>>> from incorrect argument passing with the mismatched prototype.
>>
>> Could you explain what is this '32-bit architectures ... incorrect
>> argument passing' thing?
> 
> I've expanded that paragraph now:
> 
> | Aside from the warning, this addresses a bug on 32-bit architectures
> | from incorrect argument passing with the mismatched prototype:
> | BPF_CALL_x() functions use 64-bit arguments that are passed in
> | pairs of register or on the stack on 32-bit architectures, while the
> | normal function uses one register per argument.
> 
> Let me know if you think I should put more details in there.

Please mention the function you try to address for the bug on
32-bit architecture is:

u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void 
*unsafe_ptr)

which will be incompatible with
BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
            const void *, unsafe_ptr)
in bpf_trace.c.

So you fixed this bug by using internal function 
bpf_probe_read_kernel_common() instead.

Thanks.

> 
>>> @@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code)
>>>    }
>>>    
>>>    #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>>> -u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
>>> +#ifndef CONFIG_BPF_EVENTS
>>> +int bpf_probe_read_kernel_common(void * dst, u32 size, const void *unsafe_ptr)
>>
>> void * dst => void *dst
>>
> 
> Fixed now.
> 
> Thanks,
> 
>       Arnd