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[RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs_struct structure

zhouquan@iscas.ac.cn posted 2 patches 1 year, 7 months ago
There is a newer version of this series
[RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs_struct structure
Posted by zhouquan@iscas.ac.cn 1 year, 7 months ago 
From: Quan Zhou <zhouquan@iscas.ac.cn>

Expose orig_a0 to userspace to ensure that users can modify
the actual value of `a0` in the traced process through the
ptrace(PTRACE_SETREGSET, ...) path. Since user_regs_struct is
a subset of pt_regs, we also need to adjust the position of
the orig_a0 field in pt_regs to achieve the correct copy.

Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
---
 arch/riscv/include/asm/ptrace.h      | 4 ++--
 arch/riscv/include/uapi/asm/ptrace.h | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index b5b0adcc85c1..37f48d40ae46 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -45,12 +45,12 @@ struct pt_regs {
 	unsigned long t4;
 	unsigned long t5;
 	unsigned long t6;
+	/* a0 value before the syscall */
+	unsigned long orig_a0;
 	/* Supervisor/Machine CSRs */
 	unsigned long status;
 	unsigned long badaddr;
 	unsigned long cause;
-	/* a0 value before the syscall */
-	unsigned long orig_a0;
 };
 
 #define PTRACE_SYSEMU			0x1f
diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
index a38268b19c3d..3e37f80cb3e8 100644
--- a/arch/riscv/include/uapi/asm/ptrace.h
+++ b/arch/riscv/include/uapi/asm/ptrace.h
@@ -54,6 +54,8 @@ struct user_regs_struct {
 	unsigned long t4;
 	unsigned long t5;
 	unsigned long t6;
+	/* a0 value before the syscall */
+	unsigned long orig_a0;
 };
 
 struct __riscv_f_ext_state {
-- 
2.34.1
Re: [RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs_struct structure
Posted by Charlie Jenkins 1 year, 7 months ago 
On Wed, Jun 19, 2024 at 10:01:27AM +0800, zhouquan@iscas.ac.cn wrote:
> From: Quan Zhou <zhouquan@iscas.ac.cn>
> 
> Expose orig_a0 to userspace to ensure that users can modify
> the actual value of `a0` in the traced process through the
> ptrace(PTRACE_SETREGSET, ...) path. Since user_regs_struct is
> a subset of pt_regs, we also need to adjust the position of
> the orig_a0 field in pt_regs to achieve the correct copy.
> 
> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
> ---
>  arch/riscv/include/asm/ptrace.h      | 4 ++--
>  arch/riscv/include/uapi/asm/ptrace.h | 2 ++
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
> index b5b0adcc85c1..37f48d40ae46 100644
> --- a/arch/riscv/include/asm/ptrace.h
> +++ b/arch/riscv/include/asm/ptrace.h
> @@ -45,12 +45,12 @@ struct pt_regs {
>  	unsigned long t4;
>  	unsigned long t5;
>  	unsigned long t6;
> +	/* a0 value before the syscall */
> +	unsigned long orig_a0;
>  	/* Supervisor/Machine CSRs */
>  	unsigned long status;
>  	unsigned long badaddr;
>  	unsigned long cause;
> -	/* a0 value before the syscall */
> -	unsigned long orig_a0;
>  };
>  
>  #define PTRACE_SYSEMU			0x1f
> diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
> index a38268b19c3d..3e37f80cb3e8 100644
> --- a/arch/riscv/include/uapi/asm/ptrace.h
> +++ b/arch/riscv/include/uapi/asm/ptrace.h
> @@ -54,6 +54,8 @@ struct user_regs_struct {
>  	unsigned long t4;
>  	unsigned long t5;
>  	unsigned long t6;
> +	/* a0 value before the syscall */
> +	unsigned long orig_a0;
>  };
>  
>  struct __riscv_f_ext_state {
> -- 
> 2.34.1
> 

This is a good addition!

Since orig_a0 is no longer at the bottom of pt_regs, MAX_REG_OFFSET is
now incorrect.

Can you adjust the value of:

#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)

in arch/riscv/include/asm/ptrace.h to be:

#define MAX_REG_OFFSET offsetof(struct pt_regs, cause)

This is something that is very easy to miss. I think it would be
valuable to leave a comment at the top of struct pt_regs pointing out
that MAX_REG_OFFSET needs to be adjusted if struct pt_regs changes.

- Charlie
Re: [RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs_struct structure
Posted by Quan Zhou 1 year, 7 months ago 
On 2024/6/20 09:05, Charlie Jenkins wrote:
> On Wed, Jun 19, 2024 at 10:01:27AM +0800, zhouquan@iscas.ac.cn wrote:
>> From: Quan Zhou <zhouquan@iscas.ac.cn>
>>
>> Expose orig_a0 to userspace to ensure that users can modify
>> the actual value of `a0` in the traced process through the
>> ptrace(PTRACE_SETREGSET, ...) path. Since user_regs_struct is
>> a subset of pt_regs, we also need to adjust the position of
>> the orig_a0 field in pt_regs to achieve the correct copy.
>>
>> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
>> ---
>>   arch/riscv/include/asm/ptrace.h      | 4 ++--
>>   arch/riscv/include/uapi/asm/ptrace.h | 2 ++
>>   2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
>> index b5b0adcc85c1..37f48d40ae46 100644
>> --- a/arch/riscv/include/asm/ptrace.h
>> +++ b/arch/riscv/include/asm/ptrace.h
>> @@ -45,12 +45,12 @@ struct pt_regs {
>>   	unsigned long t4;
>>   	unsigned long t5;
>>   	unsigned long t6;
>> +	/* a0 value before the syscall */
>> +	unsigned long orig_a0;
>>   	/* Supervisor/Machine CSRs */
>>   	unsigned long status;
>>   	unsigned long badaddr;
>>   	unsigned long cause;
>> -	/* a0 value before the syscall */
>> -	unsigned long orig_a0;
>>   };
>>   
>>   #define PTRACE_SYSEMU			0x1f
>> diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
>> index a38268b19c3d..3e37f80cb3e8 100644
>> --- a/arch/riscv/include/uapi/asm/ptrace.h
>> +++ b/arch/riscv/include/uapi/asm/ptrace.h
>> @@ -54,6 +54,8 @@ struct user_regs_struct {
>>   	unsigned long t4;
>>   	unsigned long t5;
>>   	unsigned long t6;
>> +	/* a0 value before the syscall */
>> +	unsigned long orig_a0;
>>   };
>>   
>>   struct __riscv_f_ext_state {
>> -- 
>> 2.34.1
>>
> This is a good addition!
>
> Since orig_a0 is no longer at the bottom of pt_regs, MAX_REG_OFFSET is
> now incorrect.
>
> Can you adjust the value of:
>
> #define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
>
> in arch/riscv/include/asm/ptrace.h to be:
>
> #define MAX_REG_OFFSET offsetof(struct pt_regs, cause)
>
> This is something that is very easy to miss. I think it would be
> valuable to leave a comment at the top of struct pt_regs pointing out
> that MAX_REG_OFFSET needs to be adjusted if struct pt_regs changes.
>
> - Charlie
>
Oh, good idea!  I'm sorry for missing such an important point earlier.

Once enough information is gathered from this RFC, I will include what 
you mentioned in the V1 series.

Thanks,
Quan
>
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Patchew 2.1-devel-b67e4c2

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