Subject: [PATCH v4 13/20] powerpc: Provide syscall wrapper

From: Rohan McLure <[email-masked]>
Date: Wed, 24 Aug 2022 12:05:41 +1000

Implement syscall wrapper as per s390, x86, arm64. When enabled
cause handlers to accept parameters from a stack frame rather than
from user scratch register state. This allows for user registers to be
safely cleared in order to reduce caller influence on speculation
within syscall routine. The wrapper is a macro that emits syscall
handler symbols that call into the target handler, obtaining its
parameters from a struct pt_regs on the stack.

As registers are already saved to the stack prior to calling
system_call_exception, it appears that this function is executed more
efficiently with the new stack-pointer convention than with parameters
passed by registers, avoiding the allocation of a stack frame for this
method. On a 32-bit system, we see >20% performance increases on the
null_syscall microbenchmark, and on a Power 8 the performance gains
amortise the cost of clearing and restoring registers which is
implemented at the end of this series, seeing final result of ~5.6%
performance improvement on null_syscall.

Syscalls are wrapped in this fashion on all platforms except for the
Cell processor as this commit does not provide SPU support. This can be
quickly fixed in a successive patch, but requires spu_sys_callback to
allocate a pt_regs structure to satisfy the wrapped calling convention.

Co-developed-by: Andrew Donnellan <[email-masked]>
Signed-off-by: Andrew Donnellan <[email-masked]>
Signed-off-by: Rohan McLure <[email-masked]>
---
V1 -> V2: Generate prototypes for symbols produced by the wrapper.
V2 -> V3: Rebased to remove conflict with 1547db7d1f44
("powerpc: Move system_call_exception() to syscall.c"). Also remove copy
from gpr3 save slot on stackframe to orig_r3's slot. Fix whitespace with
preprocessor defines in system_call_exception.
---
 arch/powerpc/Kconfig                       |  1 +
 arch/powerpc/include/asm/interrupt.h       |  3 +-
 arch/powerpc/include/asm/syscall.h         |  4 +
 arch/powerpc/include/asm/syscall_wrapper.h | 84 ++++++++++++++++++++
 arch/powerpc/include/asm/syscalls.h        | 25 +++++-
 arch/powerpc/kernel/entry_32.S             |  6 +-
 arch/powerpc/kernel/interrupt_64.S         | 16 ++--
 arch/powerpc/kernel/syscall.c              | 31 +++-----
 arch/powerpc/kernel/systbl.c               |  2 +
 arch/powerpc/kernel/vdso.c                 |  2 +
 10 files changed, 142 insertions(+), 32 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 4c466acdc70d..ef6c83e79c9b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -137,6 +137,7 @@ config PPC
 	select ARCH_HAS_STRICT_KERNEL_RWX	if (PPC_BOOK3S || PPC_8xx || 40x) && !HIBERNATION
 	select ARCH_HAS_STRICT_KERNEL_RWX	if FSL_BOOKE && !HIBERNATION && !RANDOMIZE_BASE
 	select ARCH_HAS_STRICT_MODULE_RWX	if ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_HAS_SYSCALL_WRAPPER		if !SPU_BASE
 	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UACCESS_FLUSHCACHE
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index 8069dbc4b8d1..3f9cad81585c 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -665,8 +665,7 @@ static inline void interrupt_cond_local_irq_enable(struct pt_regs *regs)
 		local_irq_enable();
 }
 
-long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8,
-			   unsigned long r0, struct pt_regs *regs);
+long system_call_exception(unsigned long r0, struct pt_regs *regs);
 notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs, long scv);
 notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs);
 notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs);
diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index d2a8dfd5de33..3dd36c5e334a 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -14,8 +14,12 @@
 #include <linux/sched.h>
 #include <linux/thread_info.h>
 
+#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
+typedef long (*syscall_fn)(const struct pt_regs *);
+#else
 typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
 			   unsigned long, unsigned long, unsigned long);
+#endif
 
 /* ftrace syscalls requires exporting the sys_call_table */
 extern const syscall_fn sys_call_table[];
diff --git a/arch/powerpc/include/asm/syscall_wrapper.h b/arch/powerpc/include/asm/syscall_wrapper.h
new file mode 100644
index 000000000000..91bcfa40f740
--- /dev/null
+++ b/arch/powerpc/include/asm/syscall_wrapper.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * syscall_wrapper.h - powerpc specific wrappers to syscall definitions
+ *
+ * Based on arch/{x86,arm64}/include/asm/syscall_wrapper.h
+ */
+
+#ifndef __ASM_SYSCALL_WRAPPER_H
+#define __ASM_SYSCALL_WRAPPER_H
+
+struct pt_regs;
+
+#define SC_POWERPC_REGS_TO_ARGS(x, ...)				\
+	__MAP(x,__SC_ARGS					\
+	      ,,regs->gpr[3],,regs->gpr[4],,regs->gpr[5]	\
+	      ,,regs->gpr[6],,regs->gpr[7],,regs->gpr[8])
+
+#ifdef CONFIG_COMPAT
+
+#define COMPAT_SYSCALL_DEFINEx(x, name, ...)						\
+	long __powerpc_compat_sys##name(const struct pt_regs *regs);			\
+	ALLOW_ERROR_INJECTION(__powerpc_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__));	\
+	long __powerpc_compat_sys##name(const struct pt_regs *regs)			\
+	{										\
+		return __se_compat_sys##name(SC_POWERPC_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)						\
+	long __powerpc_compat_sys_##sname(const struct pt_regs *__unused);	\
+	ALLOW_ERROR_INJECTION(__powerpc_compat_sys_##sname, ERRNO);		\
+	long __powerpc_compat_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL_COMPAT(name)						\
+	long __powerpc_compat_sys_##name(const struct pt_regs *regs);		\
+	long __weak __powerpc_compat_sys_##name(const struct pt_regs *regs)	\
+	{									\
+		return sys_ni_syscall();					\
+	}
+#define COMPAT_SYS_NI(name) \
+	SYSCALL_ALIAS(__powerpc_compat_sys_##name, sys_ni_posix_timers);
+
+#endif /* CONFIG_COMPAT */
+
+#define __SYSCALL_DEFINEx(x, name, ...)						\
+	long __powerpc_sys##name(const struct pt_regs *regs);			\
+	ALLOW_ERROR_INJECTION(__powerpc_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__));	\
+	long __powerpc_sys##name(const struct pt_regs *regs)			\
+	{									\
+		return __se_sys##name(SC_POWERPC_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__))
+
+#define SYSCALL_DEFINE0(sname)							\
+	SYSCALL_METADATA(_##sname, 0);						\
+	long __powerpc_sys_##sname(const struct pt_regs *__unused);		\
+	ALLOW_ERROR_INJECTION(__powerpc_sys_##sname, ERRNO);			\
+	long __powerpc_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL(name)							\
+	long __powerpc_sys_##name(const struct pt_regs *regs);			\
+	long __weak __powerpc_sys_##name(const struct pt_regs *regs)		\
+	{									\
+		return sys_ni_syscall();					\
+	}
+
+#define SYS_NI(name) SYSCALL_ALIAS(__powerpc_sys_##name, sys_ni_posix_timers);
+
+#endif /* __ASM_SYSCALL_WRAPPER_H */
diff --git a/arch/powerpc/include/asm/syscalls.h b/arch/powerpc/include/asm/syscalls.h
index e979b7593d2b..14af648ee82c 100644
--- a/arch/powerpc/include/asm/syscalls.h
+++ b/arch/powerpc/include/asm/syscalls.h
@@ -15,6 +15,12 @@
 #include <asm/unistd.h>
 #include <asm/ucontext.h>
 
+#ifndef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
+long sys_ni_syscall(void);
+#else
+long sys_ni_syscall(const struct pt_regs *regs);
+#endif
+
 struct rtas_args;
 
 #ifndef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
@@ -24,7 +30,6 @@ struct rtas_args;
  */
 
 long sys_rtas(struct rtas_args __user *uargs);
-long sys_ni_syscall(void);
 
 #ifdef CONFIG_PPC64
 long sys_ppc64_personality(unsigned long personality);
@@ -93,6 +98,24 @@ long compat_sys_ppc_sync_file_range2(int fd, unsigned int flags,
 				     unsigned int nbytes2);
 #endif /* CONFIG_COMPAT */
 
+#else
+
+#define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, native)
+#define __SYSCALL(nr, entry) \
+	long __powerpc_##entry(const struct pt_regs *regs);
+
+#ifdef CONFIG_PPC64
+#include <asm/syscall_table_64.h>
+#else
+#include <asm/syscall_table_32.h>
+#endif /* CONFIG_PPC64 */
+
+#ifdef CONFIG_COMPAT
+#undef __SYSCALL_WITH_COMPAT
+#define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
+#include <asm/syscall_table_32.h>
+#endif /* CONFIG_COMPAT */
+
 #endif /* CONFIG_ARCH_HAS_SYSCALL_WRAPPER */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 44dfce9a60c5..8d6e02ef5dc0 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -122,9 +122,9 @@ transfer_to_syscall:
 	SAVE_NVGPRS(r1)
 	kuep_lock
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	addi	r10,r1,STACK_FRAME_OVERHEAD
-	mr	r9,r0
+	/* Calling convention has r3 = orig r0, r4 = regs */
+	addi	r4,r1,STACK_FRAME_OVERHEAD
+	mr	r3,r0
 	bl	system_call_exception
 
 ret_from_syscall:
diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index 71d2d9497283..0178aeba3820 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -92,9 +92,9 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
 	std	r11,_TRAP(r1)
 	std	r12,_CCR(r1)
 	std	r3,ORIG_GPR3(r1)
-	addi	r10,r1,STACK_FRAME_OVERHEAD
+	addi	r4,r1,STACK_FRAME_OVERHEAD
 	ld	r11,exception_marker@toc(r2)
-	std	r11,-16(r10)		/* "regshere" marker */
+	std	r11,-16(r4)		/* "regshere" marker */
 
 BEGIN_FTR_SECTION
 	HMT_MEDIUM
@@ -109,8 +109,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	 * but this is the best we can do.
 	 */
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	mr	r9,r0
+	/* Calling convention has r3 = orig r0, r4 = regs */
+	mr	r3,r0
 	bl	system_call_exception
 
 .Lsyscall_vectored_\name\()_exit:
@@ -277,9 +277,9 @@ END_BTB_FLUSH_SECTION
 	std	r11,_TRAP(r1)
 	std	r12,_CCR(r1)
 	std	r3,ORIG_GPR3(r1)
-	addi	r10,r1,STACK_FRAME_OVERHEAD
+	addi	r4,r1,STACK_FRAME_OVERHEAD
 	ld	r11,exception_marker@toc(r2)
-	std	r11,-16(r10)		/* "regshere" marker */
+	std	r11,-16(r4)		/* "regshere" marker */
 
 #ifdef CONFIG_PPC_BOOK3S
 	li	r11,1
@@ -300,8 +300,8 @@ END_BTB_FLUSH_SECTION
 	wrteei	1
 #endif
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	mr	r9,r0
+	/* Calling convention has r3 = orig r0, r4 = regs */
+	mr	r3,r0
 	bl	system_call_exception
 
 .Lsyscall_exit:
diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 64102a64fd84..bda5221b420e 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -12,12 +12,8 @@
 #include <asm/unistd.h>

-typedef long (*syscall_fn)(long, long, long, long, long, long);
-
 /* Has to run notrace because it is entered not completely "reconciled" */
-notrace long system_call_exception(long r3, long r4, long r5,
-				   long r6, long r7, long r8,
-				   unsigned long r0, struct pt_regs *regs)
+notrace long system_call_exception(unsigned long r0, struct pt_regs *regs)
 {
 	long ret;
 	syscall_fn f;
@@ -138,12 +134,6 @@ notrace long system_call_exception(long r3, long r4, long r5,
 		r0 = do_syscall_trace_enter(regs);
 		if (unlikely(r0 >= NR_syscalls))
 			return regs->gpr[3];
-		r3 = regs->gpr[3];
-		r4 = regs->gpr[4];
-		r5 = regs->gpr[5];
-		r6 = regs->gpr[6];
-		r7 = regs->gpr[7];
-		r8 = regs->gpr[8];
 
 	} else if (unlikely(r0 >= NR_syscalls)) {
 		if (unlikely(trap_is_unsupported_scv(regs))) {
@@ -160,18 +150,23 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	if (unlikely(is_compat_task())) {
 		f = (void *)compat_sys_call_table[r0];
 
-		r3 &= 0x00000000ffffffffULL;
-		r4 &= 0x00000000ffffffffULL;
-		r5 &= 0x00000000ffffffffULL;
-		r6 &= 0x00000000ffffffffULL;
-		r7 &= 0x00000000ffffffffULL;
-		r8 &= 0x00000000ffffffffULL;
+		regs->gpr[3] &= 0x00000000ffffffffULL;
+		regs->gpr[4] &= 0x00000000ffffffffULL;
+		regs->gpr[5] &= 0x00000000ffffffffULL;
+		regs->gpr[6] &= 0x00000000ffffffffULL;
+		regs->gpr[7] &= 0x00000000ffffffffULL;
+		regs->gpr[8] &= 0x00000000ffffffffULL;
 
 	} else {
 		f = (void *)sys_call_table[r0];
 	}
 
-	ret = f(r3, r4, r5, r6, r7, r8);
+#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
+	ret = f(regs);
+#else
+	ret = f(regs->gpr[3], regs->gpr[4], regs->gpr[5],
+		regs->gpr[6], regs->gpr[7], regs->gpr[8]);
+#endif
 
 	/*
 	 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
diff --git a/arch/powerpc/kernel/systbl.c b/arch/powerpc/kernel/systbl.c
index b88a9c2a1f50..cb05e302ea58 100644
--- a/arch/powerpc/kernel/systbl.c
+++ b/arch/powerpc/kernel/systbl.c
@@ -15,8 +15,10 @@
 #include <asm/unistd.h>
 #include <asm/syscalls.h>
 
+#undef __SYSCALL_WITH_COMPAT
 #define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
 
+#undef __SYSCALL
 #ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
 #define __SYSCALL(nr, entry) [nr] = __powerpc_##entry,
 #define __powerpc_sys_ni_syscall	sys_ni_syscall
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 080c9e7de0c0..88d83162eaf1 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -39,6 +39,8 @@
 extern char vdso32_start, vdso32_end;
 extern char vdso64_start, vdso64_end;
 
+long sys_ni_syscall(void);
+
 /*
  * The vdso data page (aka. systemcfg for old ppc64 fans) is here.
  * Once the early boot kernel code no longer needs to muck around
-- 
2.34.1