[18/18] arm64: implement syscall wrappers

Commit Message

Mark Rutland May 14, 2018, 9:46 a.m. UTC

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 define 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.

Largely 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().

Signed-off-by: Mark Rutland <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
---
 arch/arm64/Kconfig                       |  1 +
 arch/arm64/include/asm/syscall_wrapper.h | 80 ++++++++++++++++++++++++++++++++
 arch/arm64/kernel/sys.c                  | 10 +++-
 arch/arm64/kernel/sys32.c                |  9 +++-
 arch/arm64/kernel/syscall.c              |  8 +---
 arch/arm64/kernel/traps.c                |  2 +
 6 files changed, 101 insertions(+), 9 deletions(-)
 create mode 100644 arch/arm64/include/asm/syscall_wrapper.h

Comments

Dominik Brodowski May 14, 2018, 8:57 p.m. UTC | #1

On Mon, May 14, 2018 at 10:46:40AM +0100, Mark Rutland wrote:
> 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 define 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.

> Largely the wrappers are largely the same as their x86 counterparts, but

That's one "Largely" too much.

> 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().

... for consistent naming, or is there another reason for that?

This patch looks good in any case.

Thanks,
	Dominik

Mark Rutland May 15, 2018, 8:37 a.m. UTC | #2

On Mon, May 14, 2018 at 10:57:44PM +0200, Dominik Brodowski wrote:
> On Mon, May 14, 2018 at 10:46:40AM +0100, Mark Rutland wrote:
> > 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 define 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.
> 
> > Largely the wrappers are largely the same as their x86 counterparts, but
> 
> That's one "Largely" too much.

True. I've dropped the first instance.

> > 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().
> 
> ... for consistent naming, or is there another reason for that?

For consistent naming.

I've ammended that to say:

  Unlike x86, we have some zero-argument compat syscalls, and must define
  COMPAT_SYSCALL_DEFINE0() to ensure these are also given an
  __arm64_compat_sys_ prefix.

... though I am tempted to refactor this so that our *SYSCALL_DEFINE0() and
SYSCALL_DEFINEx() share the same wrapper generation logic. The differing
prototypes don't matter per our calling convention, but IIRC some CFI features
aren't happy otherwise, and it would be nice to be consistent.

Thanks,
Mark.

Patch

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index eb2cf4938f6d..8e559b1fc555 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -21,6 +21,7 @@  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
diff --git a/arch/arm64/include/asm/syscall_wrapper.h b/arch/arm64/include/asm/syscall_wrapper.h
new file mode 100644
index 000000000000..a4477e515b79
--- /dev/null
+++ b/arch/arm64/include/asm/syscall_wrapper.h
@@ -0,0 +1,80 @@ 
+/* 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 */
diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c
index 2ad1497a184e..ee93bf789f0a 100644
--- a/arch/arm64/kernel/sys.c
+++ b/arch/arm64/kernel/sys.c
@@ -48,11 +48,17 @@  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] = sym,
+#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
 
 /*
  * The sys_call_table array must be 4K aligned to be accessible from
diff --git a/arch/arm64/kernel/sys32.c b/arch/arm64/kernel/sys32.c
index 1a84e79c47f3..8359b54a9c97 100644
--- a/arch/arm64/kernel/sys32.c
+++ b/arch/arm64/kernel/sys32.c
@@ -120,8 +120,15 @@  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] = sym,
+#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
 
 /*
  * The sys_call_table array must be 4K aligned to be accessible from
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 4706f841e758..15b5d18f6104 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -12,15 +12,11 @@ 
 
 long do_ni_syscall(struct pt_regs *regs);
 
-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);
 
 static void __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
 {
-	regs->regs[0] = syscall_fn(regs->regs[0], regs->regs[1],
-				   regs->regs[2], regs->regs[3],
-				   regs->regs[4], regs->regs[5]);
+	regs->regs[0] = syscall_fn(regs);
 }
 
 static void invoke_syscall(struct pt_regs *regs, int scno, int sc_nr,
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index b8d3e0d8c616..8bfcc37cbc65 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -549,6 +549,8 @@  asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs)
 
 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