Subject: [PATCH] arm64: ptrace: fix empty registers set in prstatus of aarch32 process core

From: [email-masked] (Will Deacon)
Date: Tue, 3 Jun 2014 15:46:02 +0100

Hi Victor,

Thanks for both the fix and the detailed explanation!

On Tue, Jun 03, 2014 at 06:46:09AM +0100, Victor Kamensky wrote:
> Currently core file of aarch32 process prstatus note has empty
> registers set. As result aarch32 core files create by V8 kernel are
> not very useful.
> 
> It happens because compat_gpr_get and compat_gpr_set functions can
> copy registers values to/from either kbuf or ubuf. ELF core file
> collection function fill_thread_core_info calls compat_gpr_get
> with kbuf set and ubuf set to 0. But current compat_gpr_get and
> compat_gpr_set function handle copy to/from only ubuf case.
> 
> Fix is to handle kbuf and ubuf as two separate cases in similar
> way as other functions like user_regset_copyout, user_regset_copyin do.

An alternative is to use set_fs when kbuf is set, then use
copy_{to,from}_user for everything. However, given how ugly I find
set_fs to start with, your patch looks good to me:

  Acked-by: Will Deacon <[email-masked]>

We probably want a CC stable too.

Cheers,

Will

> Signed-off-by: Victor Kamensky <[email-masked]>
> ---
>  arch/arm64/kernel/ptrace.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 6a8928b..9c9c2b9 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -650,11 +650,16 @@ static int compat_gpr_get(struct task_struct *target,
>  			reg = task_pt_regs(target)->regs[idx];
>  		}
>  
> -		ret = copy_to_user(ubuf, &reg, sizeof(reg));
> -		if (ret)
> -			break;
> -
> -		ubuf += sizeof(reg);
> +		if (kbuf) {
> +			memcpy(kbuf, &reg, sizeof(reg));
> +			kbuf += sizeof(reg);
> +		} else {
> +			ret = copy_to_user(ubuf, &reg, sizeof(reg));
> +			if (ret)
> +				break;
> +
> +			ubuf += sizeof(reg);
> +		}
>  	}
>  
>  	return ret;
> @@ -684,11 +689,16 @@ static int compat_gpr_set(struct task_struct *target,
>  		unsigned int idx = start + i;
>  		compat_ulong_t reg;
>  
> -		ret = copy_from_user(&reg, ubuf, sizeof(reg));
> -		if (ret)
> -			return ret;
> +		if (kbuf) {
> +			memcpy(&reg, kbuf, sizeof(reg));
> +			kbuf += sizeof(reg);
> +		} else {
> +			ret = copy_from_user(&reg, ubuf, sizeof(reg));
> +			if (ret)
> +				return ret;
>  
> -		ubuf += sizeof(reg);
> +			ubuf += sizeof(reg);
> +		}
>  
>  		switch (idx) {
>  		case 15:
> -- 
> 1.8.1.4
> 
>