[PATCHv4 19/19] arm64: implement syscall wrappers

From: Mark Rutland
Date: Mon Jul 02 2018 - 07:05:27 EST

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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: Mark Rutland <mark.rutland@xxxxxxx>
Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
---
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 | 9 ++--
5 files changed, 101 insertions(+), 8 deletions(-)
create mode 100644 arch/arm64/include/asm/syscall_wrapper.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 42c090cf0292..2089aa3f27bc 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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
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 793bd0952ee0..533c97c5c232 100644
--- a/arch/arm64/kernel/sys32.c
+++ b/arch/arm64/kernel/sys32.c
@@ -131,8 +131,15 @@ 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 ea4fc5eea182..edd822629ce4 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -14,6 +14,8 @@

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
@@ -28,14 +30,11 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
return sys_ni_syscall();
}

-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 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,
--
2.11.0

Next message: Tony Lindgren: "Re: [PATCH 1/5] ARM: dts: dra7: Disable metastability workaround for USB2"
Previous message: Mark Rutland: "[PATCHv4 17/19] arm64: use SYSCALL_DEFINE6() for mmap"
In reply to: Mark Rutland: "[PATCHv4 17/19] arm64: use SYSCALL_DEFINE6() for mmap"
Next in thread: Mark Rutland: "[PATCHv4 18/19] arm64: convert compat wrappers to C"
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