Commit 4378a7d4 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon

arm64: implement syscall wrappers

To minimize the risk of userspace-controlled values being used under
speculation, this patch adds pt_regs based syscall wrappers for arm64,
which pass the minimum set of required userspace values to syscall
implementations. For each syscall, a wrapper which takes a pt_regs
argument is automatically generated, and this extracts the arguments
before calling the "real" syscall implementation.

Each syscall has three functions generated:

* __do_<compat_>sys_<name> is the "real" syscall implementation, with
  the expected prototype.

* __se_<compat_>sys_<name> is the sign-extension/narrowing wrapper,
  inherited from common code. This takes a series of long parameters,
  casting each to the requisite types required by the "real" syscall
  implementation in __do_<compat_>sys_<name>.

  This wrapper *may* not be necessary on arm64 given the AAPCS rules on
  unused register bits, but it seemed safer to keep the wrapper for now.

* __arm64_<compat_>_sys_<name> takes a struct pt_regs pointer, and
  extracts *only* the relevant register values, passing these on to the
  __se_<compat_>sys_<name> wrapper.

The syscall invocation code is updated to handle the calling convention
required by __arm64_<compat_>_sys_<name>, and passes a single struct
pt_regs pointer.

The compiler can fold the syscall implementation and its wrappers, such
that the overhead of this approach is minimized.

Note that we play games with sys_ni_syscall(). It can't be defined with
SYSCALL_DEFINE0() because we must avoid the possibility of error
injection. Additionally, there are a couple of locations where we need
to call it from C code, and we don't (currently) have a
ksys_ni_syscall().  While it has no wrapper, passing in a redundant
pt_regs pointer is benign per the AAPCS.

When ARCH_HAS_SYSCALL_WRAPPER is selected, no prototype is defines for
sys_ni_syscall(). Since we need to treat it differently for in-kernel
calls and the syscall tables, the prototype is defined as-required.

The wrappers are largely the same as their x86 counterparts, but
simplified as we don't have a variety of compat calling conventions that
require separate stubs. Unlike x86, we have some zero-argument compat
syscalls, and must define COMPAT_SYSCALL_DEFINE0() to ensure that these
are also given an __arm64_compat_sys_ prefix.
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 55f84926
......@@ -24,6 +24,7 @@ config ARM64
select ARCH_HAS_SG_CHAIN
select ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_HAS_STRICT_MODULE_RWX
select ARCH_HAS_SYSCALL_WRAPPER
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_INLINE_READ_LOCK if !PREEMPT
......
......@@ -20,9 +20,7 @@
#include <linux/compat.h>
#include <linux/err.h>
typedef long (*syscall_fn_t)(unsigned long, unsigned long,
unsigned long, unsigned long,
unsigned long, unsigned long);
typedef long (*syscall_fn_t)(struct pt_regs *regs);
extern const syscall_fn_t sys_call_table[];
......
/* SPDX-License-Identifier: GPL-2.0 */
/*
* syscall_wrapper.h - arm64 specific wrappers to syscall definitions
*
* Based on arch/x86/include/asm_syscall_wrapper.h
*/
#ifndef __ASM_SYSCALL_WRAPPER_H
#define __ASM_SYSCALL_WRAPPER_H
#define SC_ARM64_REGS_TO_ARGS(x, ...) \
__MAP(x,__SC_ARGS \
,,regs->regs[0],,regs->regs[1],,regs->regs[2] \
,,regs->regs[3],,regs->regs[4],,regs->regs[5])
#ifdef CONFIG_COMPAT
#define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long __arm64_compat_sys##name(const struct pt_regs *regs); \
ALLOW_ERROR_INJECTION(__arm64_compat_sys##name, ERRNO); \
static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
asmlinkage long __arm64_compat_sys##name(const struct pt_regs *regs) \
{ \
return __se_compat_sys##name(SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__)); \
} \
static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
} \
static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
#define COMPAT_SYSCALL_DEFINE0(sname) \
asmlinkage long __arm64_compat_sys_##sname(void); \
ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO); \
asmlinkage long __arm64_compat_sys_##sname(void)
#define COND_SYSCALL_COMPAT(name) \
cond_syscall(__arm64_compat_sys_##name);
#define COMPAT_SYS_NI(name) \
SYSCALL_ALIAS(__arm64_compat_sys_##name, sys_ni_posix_timers);
#endif /* CONFIG_COMPAT */
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long __arm64_sys##name(const struct pt_regs *regs); \
ALLOW_ERROR_INJECTION(__arm64_sys##name, ERRNO); \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
asmlinkage long __arm64_sys##name(const struct pt_regs *regs) \
{ \
return __se_sys##name(SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__)); \
} \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
__MAP(x,__SC_TEST,__VA_ARGS__); \
__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
return ret; \
} \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
#ifndef SYSCALL_DEFINE0
#define SYSCALL_DEFINE0(sname) \
SYSCALL_METADATA(_##sname, 0); \
asmlinkage long __arm64_sys_##sname(void); \
ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO); \
asmlinkage long __arm64_sys_##sname(void)
#endif
#ifndef COND_SYSCALL
#define COND_SYSCALL(name) cond_syscall(__arm64_sys_##name)
#endif
#ifndef SYS_NI
#define SYS_NI(name) SYSCALL_ALIAS(__arm64_sys_##name, sys_ni_posix_timers);
#endif
#endif /* __ASM_SYSCALL_WRAPPER_H */
......@@ -50,11 +50,17 @@ SYSCALL_DEFINE1(arm64_personality, unsigned int, personality)
/*
* Wrappers to pass the pt_regs argument.
*/
asmlinkage long sys_rt_sigreturn(void);
#define sys_personality sys_arm64_personality
asmlinkage long sys_ni_syscall(const struct pt_regs *);
#define __arm64_sys_ni_syscall sys_ni_syscall
#undef __SYSCALL
#define __SYSCALL(nr, sym) asmlinkage long __arm64_##sym(const struct pt_regs *);
#include <asm/unistd.h>
#undef __SYSCALL
#define __SYSCALL(nr, sym) [nr] = (syscall_fn_t)sym,
#define __SYSCALL(nr, sym) [nr] = (syscall_fn_t)__arm64_##sym,
const syscall_fn_t sys_call_table[__NR_syscalls] = {
[0 ... __NR_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
......
......@@ -133,8 +133,15 @@ COMPAT_SYSCALL_DEFINE6(aarch32_fallocate, int, fd, int, mode,
return ksys_fallocate(fd, mode, arg_u64(offset), arg_u64(len));
}
asmlinkage long sys_ni_syscall(const struct pt_regs *);
#define __arm64_sys_ni_syscall sys_ni_syscall
#undef __SYSCALL
#define __SYSCALL(nr, sym) asmlinkage long __arm64_##sym(const struct pt_regs *);
#include <asm/unistd32.h>
#undef __SYSCALL
#define __SYSCALL(nr, sym) [nr] = (syscall_fn_t)sym,
#define __SYSCALL(nr, sym) [nr] = (syscall_fn_t)__arm64_##sym,
const syscall_fn_t compat_sys_call_table[__NR_compat_syscalls] = {
[0 ... __NR_compat_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
......
......@@ -15,6 +15,8 @@
long compat_arm_syscall(struct pt_regs *regs);
long sys_ni_syscall(void);
asmlinkage long do_ni_syscall(struct pt_regs *regs)
{
#ifdef CONFIG_COMPAT
......@@ -31,8 +33,7 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
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]);
return syscall_fn(regs);
}
static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
......
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