Commit 4141c857 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

arm64: convert raw syscall invocation to C 



As a first step towards invoking syscalls with a pt_regs argument,
convert the raw syscall invocation logic to C. We end up with a bit more
register shuffling, but the unified invocation logic means we can unify
the tracing paths, too.

Previously, assembly had to open-code calls to ni_sys() when the system
call number was out-of-bounds for the relevant syscall table. This case
is now handled by invoke_syscall(), and the assembly no longer need to
handle this case explicitly. This allows the tracing paths to be
simplified and unified, as we no longer need the __ni_sys_trace path and
the __sys_trace_return label.

This only converts the invocation of the syscall. The rest of the
syscall triage and tracing is left in assembly for now, and will be
converted in subsequent patches.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 27d83e68

arch/arm64/kernel/Makefile

+2 −1
Original line number Diff line number Diff line
@@ -18,7 +18,8 @@ arm64-obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ 
			   hyp-stub.o psci.o cpu_ops.o insn.o	\

			   return_address.o cpuinfo.o cpu_errata.o		\

			   cpufeature.o alternative.o cacheinfo.o		\

			   smp.o smp_spin_table.o topology.o smccc-call.o

			   smp.o smp_spin_table.o topology.o smccc-call.o	\

			   syscall.o



extra-$(CONFIG_EFI)			:= efi-entry.o

arch/arm64/kernel/entry.S

+10 −26
Original line number Diff line number Diff line
@@ -903,7 +903,6 @@ ENDPROC(el0_error) 
 */

ret_fast_syscall:

	disable_daif

	str	x0, [sp, #S_X0]			// returned x0

#ifndef CONFIG_DEBUG_RSEQ

	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing

	and	x2, x1, #_TIF_SYSCALL_WORK
@@ -978,15 +977,11 @@ el0_svc_naked: // compat entry point 


	tst	x16, #_TIF_SYSCALL_WORK		// check for syscall hooks

	b.ne	__sys_trace

	cmp     wscno, wsc_nr			// check upper syscall limit

	b.hs	ni_sys

	mask_nospec64 xscno, xsc_nr, x19	// enforce bounds for syscall number

	ldr	x16, [stbl, xscno, lsl #3]	// address in the syscall table

	blr	x16				// call sys_* routine

	b	ret_fast_syscall

ni_sys:

	mov	x0, sp

	bl	do_ni_syscall

	mov	w1, wscno

	mov	w2, wsc_nr

	mov	x3, stbl

	bl	invoke_syscall

	b	ret_fast_syscall

ENDPROC(el0_svc)
@@ -1003,29 +998,18 @@ __sys_trace: 
	bl	syscall_trace_enter

	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

	cmp	wscno, wsc_nr			// check upper syscall limit

	b.hs	__ni_sys_trace

	ldp	x0, x1, [sp]			// restore the syscall args

	ldp	x2, x3, [sp, #S_X2]

	ldp	x4, x5, [sp, #S_X4]

	ldp	x6, x7, [sp, #S_X6]

	ldr	x16, [stbl, xscno, lsl #3]	// address in the syscall table

	blr	x16				// call sys_* routine



__sys_trace_return:

	str	x0, [sp, #S_X0]			// save returned x0

	mov	x0, sp

	mov	w1, wscno

	mov	w2, wsc_nr

	mov	x3, stbl

	bl	invoke_syscall



__sys_trace_return_skipped:

	mov	x0, sp

	bl	syscall_trace_exit

	b	ret_to_user



__ni_sys_trace:

	mov	x0, sp

	bl	do_ni_syscall

	b	__sys_trace_return



	.popsection				// .entry.text



#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

arch/arm64/kernel/syscall.c

0 → 100644
+47 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0



#include <linux/errno.h>

#include <linux/nospec.h>

#include <linux/ptrace.h>

#include <linux/syscalls.h>



#include <asm/syscall.h>



long compat_arm_syscall(struct pt_regs *regs);



asmlinkage long do_ni_syscall(struct pt_regs *regs)

{

#ifdef CONFIG_COMPAT

	long ret;

	if (is_compat_task()) {

		ret = compat_arm_syscall(regs);

		if (ret != -ENOSYS)

			return ret;

	}

#endif



	return sys_ni_syscall();

}



static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)

{

	return syscall_fn(regs->regs[0], regs->regs[1], regs->regs[2],

			  regs->regs[3], regs->regs[4], regs->regs[5]);

}



asmlinkage void invoke_syscall(struct pt_regs *regs, unsigned int scno,

			       unsigned int sc_nr,

			       const syscall_fn_t syscall_table[])

{

	long ret;



	if (scno < sc_nr) {

		syscall_fn_t syscall_fn;

		syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];

		ret = __invoke_syscall(regs, syscall_fn);

	} else {

		ret = do_ni_syscall(regs);

	}



	regs->regs[0] = ret;

}

arch/arm64/kernel/traps.c

+0 −16
Original line number Diff line number Diff line
@@ -547,22 +547,6 @@ asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs) 
	do_undefinstr(regs);

}



long compat_arm_syscall(struct pt_regs *regs);



asmlinkage long do_ni_syscall(struct pt_regs *regs)

{

#ifdef CONFIG_COMPAT

	long ret;

	if (is_compat_task()) {

		ret = compat_arm_syscall(regs);

		if (ret != -ENOSYS)

			return ret;

	}

#endif



	return sys_ni_syscall();

}



static const char *esr_class_str[] = {

	[0 ... ESR_ELx_EC_MAX]		= "UNRECOGNIZED EC",

	[ESR_ELx_EC_UNKNOWN]		= "Unknown/Uncategorized",

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