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arm64: Abstract syscallno manipulation

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The -1 "no syscall" value is written in various ways, shared with
the user ABI in some places, and generally obscure.

This patch attempts to make things a little more consistent and
readable by replacing all these uses with a single #define.  A
couple of symbolic helpers are provided to clarify the intent
further.

Because the in-syscall check in do_signal() is changed from >= 0 to
!= NO_SYSCALL by this patch, different behaviour may be observable
if syscallno is set to values less than -1 by a tracer.  However,
this is not different from the behaviour that is already observable
if a tracer sets syscallno to a value >= __NR_(compat_)syscalls.

It appears that this can cause spurious syscall restarting, but
that is not a new behaviour either, and does not appear harmful.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Dave Martin
2017-08-01 15:35:54 +01:00
committed by Catalin Marinas
parent 35d0e6fb4d
commit 17c2895860
6 changed files with 33 additions and 14 deletions
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10
arch/arm64/kernel/signal.c
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@@ -36,6 +36,7 @@
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/fpsimd.h>
#include <asm/ptrace.h>
#include <asm/signal32.h>
#include <asm/vdso.h>
@@ -387,7 +388,7 @@ static int restore_sigframe(struct pt_regs *regs,
/*
* Avoid sys_rt_sigreturn() restarting.
*/
regs->syscallno = ~0;
forget_syscall(regs);
err |= !valid_user_regs(&regs->user_regs, current);
if (err == 0)
@@ -673,13 +674,12 @@ static void do_signal(struct pt_regs *regs)
{
unsigned long continue_addr = 0, restart_addr = 0;
int retval = 0;
int syscall = regs->syscallno;
struct ksignal ksig;
/*
* If we were from a system call, check for system call restarting...
*/
if (syscall >= 0) {
if (in_syscall(regs)) {
continue_addr = regs->pc;
restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);
retval = regs->regs[0];
@@ -687,7 +687,7 @@ static void do_signal(struct pt_regs *regs)
/*
* Avoid additional syscall restarting via ret_to_user.
*/
regs->syscallno = ~0;
forget_syscall(regs);
/*
* Prepare for system call restart. We do this here so that a
@@ -731,7 +731,7 @@ static void do_signal(struct pt_regs *regs)
* Handle restarting a different system call. As above, if a debugger
* has chosen to restart at a different PC, ignore the restart.
*/
if (syscall >= 0 && regs->pc == restart_addr) {
if (in_syscall(regs) && regs->pc == restart_addr) {
if (retval == -ERESTART_RESTARTBLOCK)
setup_restart_syscall(regs);
user_rewind_single_step(current);