Re: [PATCH 1/3] arm64: ptrace: Add is_syscall_success to handle compat
On 4/16/21 8:33 PM, Catalin Marinas wrote:
On Fri, Apr 16, 2021 at 03:55:31PM +0800, He Zhe wrote:
> The general version of is_syscall_success does not handle 32-bit
> compatible case, which would cause 32-bit negative return code to be
> recoganized as a positive number later and seen as a "success".
> Since is_compat_thread is defined in compat.h,
implementing
> is_syscall_success in ptrace.h would introduce build failure due to
> recursive inclusion of some basic headers like mutex.h. We put the
> implementation to ptrace.c
> Signed-off-by: He Zhe <zhe.he(a)windriver.com > ---
> arch/arm64/include/asm/ptrace.h | 3 +++
> arch/arm64/kernel/ptrace.c | 10 ++++++++++
> 2 files changed, 13 insertions(+)
> diff --git a/arch/arm64/include/asm/ptrace.h
b/arch/arm64/include/asm/ptrace.h
> index e58bca832dff..3c415e9e5d85 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -328,6 +328,9 @@ static inline void regs_set_return_value(struct pt_regs *regs,
unsigned long rc)
> regs->regs[0] = rc;
> }
>
> +extern inline int is_syscall_success(struct pt_regs *regs);
> +#define is_syscall_success(regs) is_syscall_success(regs)
> +
> /**
> * regs_get_kernel_argument() - get Nth function argument in kernel
> * @regs: pt_regs of that context
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 170f42fd6101..3266201f8c60 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -1909,3 +1909,13 @@ int valid_user_regs(struct user_pt_regs *regs, struct
task_struct *task)
> else
> return valid_native_regs(regs);
> }
> +
> +inline int is_syscall_success(struct pt_regs *regs)
> +{
> + unsigned long val = regs->regs[0];
> +
> + if (is_compat_thread(task_thread_info(current)))
> + val = sign_extend64(val, 31);
> +
> + return !IS_ERR_VALUE(val);
> +}
It's better to use compat_user_mode(regs) here instead of
is_compat_thread(). It saves us from worrying whether regs are for the
current context.
Thanks. I'll use this for v2.
I think we should change regs_return_value() instead. This function
seems to be called from several other places and it has the same
potential problems if called on compat pt_regs.
IMHO, now that we have had specific function, syscall_get_return_value, to get
syscall return code, we might as well use it. regs_return_value may be left for
where we want internal return code. I found such places below and haven't found
other places that syscall sign extension is concerned about.
kernel/test_kprobes.c
kernel/trace/trace_kprobe.c
samples/kprobes/kretprobe_example.c
Regards,
Zhe