Re: [PATCH 07/18] arm64: remove sigreturn wrappers

From: Dave Martin
Date: Mon May 14 2018 - 07:07:14 EST

On Mon, May 14, 2018 at 10:46:29AM +0100, Mark Rutland wrote:
> The arm64 sigreturn* syscall handlers are non-standard. Rather than
> taking a number of user parameters in registers as per the AAPCS,
> they expect the pt_regs as their sole argument.
>
> To make this work, we override the syscall definitions to invoke
> wrappers written in assembly, which mov the SP into x0, and branch to
> their respective C functions.
>
> On other architectures (such as x86), the sigreturn* functions take no
> argument and instead use current_pt_regs() to acquire the user
> registers. This requires less boilerplate code, and allows for other
> features such as interposing C code in this path.

Hmmm, I always wondered why rt_sigreturn() et al. were handled
specially.

If there's effectively no underlying reason for that, it makes sense
to regularise the interface to these syscalls.

Tentatively-reviewed-by: Dave Martin <Dave.Martin@xxxxxxx>

>
> This patch takes the same approach for arm64.
>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
> arch/arm64/include/asm/unistd32.h | 4 ++--
> arch/arm64/kernel/entry.S | 8 --------
> arch/arm64/kernel/entry32.S | 10 ----------
> arch/arm64/kernel/signal.c | 3 ++-
> arch/arm64/kernel/signal32.c | 6 ++++--
> arch/arm64/kernel/sys.c | 3 +--
> arch/arm64/kernel/sys32.c | 4 ++--
> 7 files changed, 11 insertions(+), 27 deletions(-)
>
> diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
> index ef292160748c..ab95554b1734 100644
> --- a/arch/arm64/include/asm/unistd32.h
> +++ b/arch/arm64/include/asm/unistd32.h
> @@ -260,7 +260,7 @@ __SYSCALL(117, sys_ni_syscall)
> #define __NR_fsync 118
> __SYSCALL(__NR_fsync, sys_fsync)
> #define __NR_sigreturn 119
> -__SYSCALL(__NR_sigreturn, compat_sys_sigreturn_wrapper)
> +__SYSCALL(__NR_sigreturn, compat_sys_sigreturn)
> #define __NR_clone 120
> __SYSCALL(__NR_clone, sys_clone)
> #define __NR_setdomainname 121
> @@ -368,7 +368,7 @@ __SYSCALL(__NR_getresgid, sys_getresgid16)
> #define __NR_prctl 172
> __SYSCALL(__NR_prctl, sys_prctl)
> #define __NR_rt_sigreturn 173
> -__SYSCALL(__NR_rt_sigreturn, compat_sys_rt_sigreturn_wrapper)
> +__SYSCALL(__NR_rt_sigreturn, compat_sys_rt_sigreturn)
> #define __NR_rt_sigaction 174
> __SYSCALL(__NR_rt_sigaction, compat_sys_rt_sigaction)
> #define __NR_rt_sigprocmask 175
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index ec2ee720e33e..08ea3cbfb08f 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -1108,14 +1108,6 @@ __entry_tramp_data_start:
> #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
>
> /*
> - * Special system call wrappers.
> - */
> -ENTRY(sys_rt_sigreturn_wrapper)
> - mov x0, sp
> - b sys_rt_sigreturn
> -ENDPROC(sys_rt_sigreturn_wrapper)
> -
> -/*
> * Register switch for AArch64. The callee-saved registers need to be saved
> * and restored. On entry:
> * x0 = previous task_struct (must be preserved across the switch)
> diff --git a/arch/arm64/kernel/entry32.S b/arch/arm64/kernel/entry32.S
> index f332d5d1f6b4..f9461696dde4 100644
> --- a/arch/arm64/kernel/entry32.S
> +++ b/arch/arm64/kernel/entry32.S
> @@ -30,16 +30,6 @@
> * System call wrappers for the AArch32 compatibility layer.
> */
>
> -ENTRY(compat_sys_sigreturn_wrapper)
> - mov x0, sp
> - b compat_sys_sigreturn
> -ENDPROC(compat_sys_sigreturn_wrapper)
> -
> -ENTRY(compat_sys_rt_sigreturn_wrapper)
> - mov x0, sp
> - b compat_sys_rt_sigreturn
> -ENDPROC(compat_sys_rt_sigreturn_wrapper)
> -
> ENTRY(compat_sys_statfs64_wrapper)
> mov w3, #84
> cmp w1, #88
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 8e624fec4707..caa7a68cf2d2 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -538,8 +538,9 @@ static int restore_sigframe(struct pt_regs *regs,
> return err;
> }
>
> -asmlinkage long sys_rt_sigreturn(struct pt_regs *regs)
> +asmlinkage long sys_rt_sigreturn(void)
> {
> + struct pt_regs *regs = current_pt_regs();
> struct rt_sigframe __user *frame;
>
> /* Always make any pending restarted system calls return -EINTR */
> diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
> index 77b91f478995..cb10588a7cb2 100644
> --- a/arch/arm64/kernel/signal32.c
> +++ b/arch/arm64/kernel/signal32.c
> @@ -282,8 +282,9 @@ static int compat_restore_sigframe(struct pt_regs *regs,
> return err;
> }
>
> -asmlinkage int compat_sys_sigreturn(struct pt_regs *regs)
> +asmlinkage int compat_sys_sigreturn(void)
> {
> + struct pt_regs *regs = current_pt_regs();
> struct compat_sigframe __user *frame;
>
> /* Always make any pending restarted system calls return -EINTR */
> @@ -312,8 +313,9 @@ asmlinkage int compat_sys_sigreturn(struct pt_regs *regs)
> return 0;
> }
>
> -asmlinkage int compat_sys_rt_sigreturn(struct pt_regs *regs)
> +asmlinkage int compat_sys_rt_sigreturn(void)
> {
> + struct pt_regs *regs = current_pt_regs();
> struct compat_rt_sigframe __user *frame;
>
> /* Always make any pending restarted system calls return -EINTR */
> diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c
> index 72981bae10eb..31045f3fed92 100644
> --- a/arch/arm64/kernel/sys.c
> +++ b/arch/arm64/kernel/sys.c
> @@ -48,8 +48,7 @@ SYSCALL_DEFINE1(arm64_personality, unsigned int, personality)
> /*
> * Wrappers to pass the pt_regs argument.
> */
> -asmlinkage long sys_rt_sigreturn_wrapper(void);
> -#define sys_rt_sigreturn sys_rt_sigreturn_wrapper
> +asmlinkage long sys_rt_sigreturn(void);
> #define sys_personality sys_arm64_personality
>
> #undef __SYSCALL
> diff --git a/arch/arm64/kernel/sys32.c b/arch/arm64/kernel/sys32.c
> index a40b1343b819..1ef103c95410 100644
> --- a/arch/arm64/kernel/sys32.c
> +++ b/arch/arm64/kernel/sys32.c
> @@ -25,8 +25,8 @@
> #include <linux/compiler.h>
> #include <linux/syscalls.h>
>
> -asmlinkage long compat_sys_sigreturn_wrapper(void);
> -asmlinkage long compat_sys_rt_sigreturn_wrapper(void);
> +asmlinkage long compat_sys_sigreturn(void);
> +asmlinkage long compat_sys_rt_sigreturn(void);
> asmlinkage long compat_sys_statfs64_wrapper(void);
> asmlinkage long compat_sys_fstatfs64_wrapper(void);
> asmlinkage long compat_sys_pread64_wrapper(void);
> --
> 2.11.0
>
>
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