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Commit 17c28958 authored by Dave Martin's avatar Dave Martin Committed by Catalin Marinas
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arm64: Abstract syscallno manipulation 



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: default avatarDave Martin <Dave.Martin@arm.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 35d0e6fb

arch/arm64/include/asm/processor.h

+1 −1
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ void tls_preserve_current_state(void); 
static inline void start_thread_common(struct pt_regs *regs, unsigned long pc)

{

	memset(regs, 0, sizeof(*regs));

	regs->syscallno = ~0;

	forget_syscall(regs);

	regs->pc = pc;

}

arch/arm64/include/asm/ptrace.h

+21 −0
Original line number Diff line number Diff line
@@ -72,8 +72,19 @@ 
#define COMPAT_PT_TEXT_ADDR		0x10000

#define COMPAT_PT_DATA_ADDR		0x10004

#define COMPAT_PT_TEXT_END_ADDR		0x10008



/*

 * If pt_regs.syscallno == NO_SYSCALL, then the thread is not executing

 * a syscall -- i.e., its most recent entry into the kernel from

 * userspace was not via SVC, or otherwise a tracer cancelled the syscall.

 *

 * This must have the value -1, for ABI compatibility with ptrace etc.

 */

#define NO_SYSCALL (-1)



#ifndef __ASSEMBLY__

#include <linux/bug.h>

#include <linux/types.h>



/* sizeof(struct user) for AArch32 */

#define COMPAT_USER_SZ	296
@@ -128,6 +139,16 @@ struct pt_regs { 
	u64 unused;	// maintain 16 byte alignment

};



static inline bool in_syscall(struct pt_regs const *regs)

{

	return regs->syscallno != NO_SYSCALL;

}



static inline void forget_syscall(struct pt_regs *regs)

{

	regs->syscallno = NO_SYSCALL;

}



#define MAX_REG_OFFSET offsetof(struct pt_regs, pstate)



#define arch_has_single_step()	(1)

arch/arm64/kernel/entry.S

+4 −6
Original line number Diff line number Diff line
@@ -138,11 +138,9 @@ alternative_else_nop_endif 


	stp	x22, x23, [sp, #S_PC]



	/*

	 * Set syscallno to -1 by default (overridden later if real syscall).

	 */

	/* Not in a syscall by default (el0_svc overwrites for real syscall) */

	.if	\el == 0

	mvn	w21, wzr

	mov	w21, #NO_SYSCALL

	str	w21, [sp, #S_SYSCALLNO]

	.endif
@@ -825,13 +823,13 @@ ENDPROC(el0_svc) 
	 * switches, and waiting for our parent to respond.

	 */

__sys_trace:

	cmp     wscno, #-1			// user-issued syscall(-1)?

	cmp     wscno, #NO_SYSCALL		// user-issued syscall(-1)?

	b.ne	1f

	mov	x0, #-ENOSYS			// set default errno if so

	str	x0, [sp, #S_X0]

1:	mov	x0, sp

	bl	syscall_trace_enter

	cmp	w0, #-1				// skip the syscall?

	cmp	w0, #NO_SYSCALL			// skip the syscall?

	b.eq	__sys_trace_return_skipped

	mov	wscno, w0			// syscall number (possibly new)

	mov	x1, sp				// pointer to regs

arch/arm64/kernel/ptrace.c

+1 −1
Original line number Diff line number Diff line
@@ -1363,7 +1363,7 @@ static void tracehook_report_syscall(struct pt_regs *regs, 
	if (dir == PTRACE_SYSCALL_EXIT)

		tracehook_report_syscall_exit(regs, 0);

	else if (tracehook_report_syscall_entry(regs))

		regs->syscallno = ~0;

		forget_syscall(regs);



	regs->regs[regno] = saved_reg;

}

arch/arm64/kernel/signal.c

+5 −5
Original line number Diff line number Diff line
@@ -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);