Subject: [PATCH 11/12] riscv: extable: add a dedicated uaccess handler

From: Jisheng Zhang <[email-masked]>
Date: Thu, 18 Nov 2021 19:26:51 +0800

From: Jisheng Zhang <[email-masked]>

Inspired by commit 2e77a62cb3a6("arm64: extable: add a dedicated
uaccess handler"), do similar to riscv to add a dedicated uaccess
exception handler to update registers in exception context and
subsequently return back into the function which faulted, so we remove
the need for fixups specialized to each faulting instruction.

Signed-off-by: Jisheng Zhang <[email-masked]>
---
 arch/riscv/include/asm/asm-extable.h | 23 +++++++++
 arch/riscv/include/asm/futex.h       | 23 +++------
 arch/riscv/include/asm/uaccess.h     | 74 +++++++++-------------------
 arch/riscv/mm/extable.c              | 27 ++++++++++
 4 files changed, 78 insertions(+), 69 deletions(-)

diff --git a/arch/riscv/include/asm/asm-extable.h b/arch/riscv/include/asm/asm-extable.h
index 1b1f4ffd8d37..14be0673f5b5 100644
--- a/arch/riscv/include/asm/asm-extable.h
+++ b/arch/riscv/include/asm/asm-extable.h
@@ -5,6 +5,7 @@
 #define EX_TYPE_NONE			0
 #define EX_TYPE_FIXUP			1
 #define EX_TYPE_BPF			2
+#define EX_TYPE_UACCESS_ERR_ZERO	3
 
 #ifdef __ASSEMBLY__
 
@@ -23,7 +24,9 @@
 
 #else /* __ASSEMBLY__ */
 
+#include <linux/bits.h>
 #include <linux/stringify.h>
+#include <asm/gpr-num.h>
 
 #define __ASM_EXTABLE_RAW(insn, fixup, type, data)	\
 	".pushsection	__ex_table, \"a\"\n"		\
@@ -37,6 +40,26 @@
 #define _ASM_EXTABLE(insn, fixup)	\
 	__ASM_EXTABLE_RAW(#insn, #fixup, __stringify(EX_TYPE_FIXUP), "0")
 
+#define EX_DATA_REG_ERR_SHIFT	0
+#define EX_DATA_REG_ERR		GENMASK(4, 0)
+#define EX_DATA_REG_ZERO_SHIFT	5
+#define EX_DATA_REG_ZERO	GENMASK(9, 5)
+
+#define EX_DATA_REG(reg, gpr)						\
+	"((.L__gpr_num_" #gpr ") << " __stringify(EX_DATA_REG_##reg##_SHIFT) ")"
+
+#define _ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, zero)		\
+	__DEFINE_ASM_GPR_NUMS						\
+	__ASM_EXTABLE_RAW(#insn, #fixup, 				\
+			  __stringify(EX_TYPE_UACCESS_ERR_ZERO),	\
+			  "("						\
+			    EX_DATA_REG(ERR, err) " | "			\
+			    EX_DATA_REG(ZERO, zero)			\
+			  ")")
+
+#define _ASM_EXTABLE_UACCESS_ERR(insn, fixup, err)			\
+	_ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, zero)
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __ASM_ASM_EXTABLE_H */
diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
index 2e15e8e89502..fc8130f995c1 100644
--- a/arch/riscv/include/asm/futex.h
+++ b/arch/riscv/include/asm/futex.h
@@ -21,20 +21,14 @@
 
 #define __futex_atomic_op(insn, ret, oldval, uaddr, oparg)	\
 {								\
-	uintptr_t tmp;						\
 	__enable_user_access();					\
 	__asm__ __volatile__ (					\
 	"1:	" insn "				\n"	\
 	"2:						\n"	\
-	"	.section .fixup,\"ax\"			\n"	\
-	"	.balign 4				\n"	\
-	"3:	li %[r],%[e]				\n"	\
-	"	jump 2b,%[t]				\n"	\
-	"	.previous				\n"	\
-		_ASM_EXTABLE(1b, 3b)				\
+	_ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r])			\
 	: [r] "+r" (ret), [ov] "=&r" (oldval),			\
-	  [u] "+m" (*uaddr), [t] "=&r" (tmp)			\
-	: [op] "Jr" (oparg), [e] "i" (-EFAULT)			\
+	  [u] "+m" (*uaddr)					\
+	: [op] "Jr" (oparg)					\
 	: "memory");						\
 	__disable_user_access();				\
 }
@@ -96,15 +90,10 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	"2:	sc.w.aqrl %[t],%z[nv],%[u]		\n"
 	"	bnez %[t],1b				\n"
 	"3:						\n"
-	"	.section .fixup,\"ax\"			\n"
-	"	.balign 4				\n"
-	"4:	li %[r],%[e]				\n"
-	"	jump 3b,%[t]				\n"
-	"	.previous				\n"
-		_ASM_EXTABLE(1b, 4b)			\
-		_ASM_EXTABLE(2b, 4b)			\
+		_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %[r])	\
+		_ASM_EXTABLE_UACCESS_ERR(2b, 3b, %[r])	\
 	: [r] "+r" (ret), [v] "=&r" (val), [u] "+m" (*uaddr), [t] "=&r" (tmp)
-	: [ov] "Jr" (oldval), [nv] "Jr" (newval), [e] "i" (-EFAULT)
+	: [ov] "Jr" (oldval), [nv] "Jr" (newval)
 	: "memory");
 	__disable_user_access();
 
diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index 40e6099af488..a4716c026386 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -81,22 +81,14 @@ static inline int __access_ok(unsigned long addr, unsigned long size)
 
 #define __get_user_asm(insn, x, ptr, err)			\
 do {								\
-	uintptr_t __tmp;					\
 	__typeof__(x) __x;					\
 	__asm__ __volatile__ (					\
 		"1:\n"						\
-		"	" insn " %1, %3\n"			\
+		"	" insn " %1, %2\n"			\
 		"2:\n"						\
-		"	.section .fixup,\"ax\"\n"		\
-		"	.balign 4\n"				\
-		"3:\n"						\
-		"	li %0, %4\n"				\
-		"	li %1, 0\n"				\
-		"	jump 2b, %2\n"				\
-		"	.previous\n"				\
-			_ASM_EXTABLE(1b, 3b)			\
-		: "+r" (err), "=&r" (__x), "=r" (__tmp)		\
-		: "m" (*(ptr)), "i" (-EFAULT));			\
+		_ASM_EXTABLE_UACCESS_ERR_ZERO(1b, 2b, %0, %1)	\
+		: "+r" (err), "=&r" (__x)			\
+		: "m" (*(ptr)));				\
 	(x) = __x;						\
 } while (0)
 
@@ -108,27 +100,18 @@ do {								\
 do {								\
 	u32 __user *__ptr = (u32 __user *)(ptr);		\
 	u32 __lo, __hi;						\
-	uintptr_t __tmp;					\
 	__asm__ __volatile__ (					\
 		"1:\n"						\
-		"	lw %1, %4\n"				\
+		"	lw %1, %3\n"				\
 		"2:\n"						\
-		"	lw %2, %5\n"				\
+		"	lw %2, %4\n"				\
 		"3:\n"						\
-		"	.section .fixup,\"ax\"\n"		\
-		"	.balign 4\n"				\
-		"4:\n"						\
-		"	li %0, %6\n"				\
-		"	li %1, 0\n"				\
-		"	li %2, 0\n"				\
-		"	jump 3b, %3\n"				\
-		"	.previous\n"				\
-			_ASM_EXTABLE(1b, 4b)			\
-			_ASM_EXTABLE(2b, 4b)			\
-		: "+r" (err), "=&r" (__lo), "=r" (__hi),	\
-			"=r" (__tmp)				\
-		: "m" (__ptr[__LSW]), "m" (__ptr[__MSW]),	\
-			"i" (-EFAULT));				\
+		_ASM_EXTABLE_UACCESS_ERR_ZERO(1b, 3b, %0, %1)	\
+		_ASM_EXTABLE_UACCESS_ERR_ZERO(2b, 3b, %0, %1)	\
+		: "+r" (err), "=&r" (__lo), "=r" (__hi)		\
+		: "m" (__ptr[__LSW]), "m" (__ptr[__MSW]))	\
+	if (err)						\
+		__hi = 0;					\
 	(x) = (__typeof__(x))((__typeof__((x)-(x)))(		\
 		(((u64)__hi << 32) | __lo)));			\
 } while (0)
@@ -216,21 +199,14 @@ do {								\
 
 #define __put_user_asm(insn, x, ptr, err)			\
 do {								\
-	uintptr_t __tmp;					\
 	__typeof__(*(ptr)) __x = x;				\
 	__asm__ __volatile__ (					\
 		"1:\n"						\
-		"	" insn " %z3, %2\n"			\
+		"	" insn " %z2, %1\n"			\
 		"2:\n"						\
-		"	.section .fixup,\"ax\"\n"		\
-		"	.balign 4\n"				\
-		"3:\n"						\
-		"	li %0, %4\n"				\
-		"	jump 2b, %1\n"				\
-		"	.previous\n"				\
-			_ASM_EXTABLE(1b, 3b)			\
-		: "+r" (err), "=r" (__tmp), "=m" (*(ptr))	\
-		: "rJ" (__x), "i" (-EFAULT));			\
+		_ASM_EXTABLE_UACCESS_ERR(1b, 2b, %0)		\
+		: "+r" (err), "=m" (*(ptr))			\
+		: "rJ" (__x));					\
 } while (0)
 
 #ifdef CONFIG_64BIT
@@ -244,22 +220,16 @@ do {								\
 	uintptr_t __tmp;					\
 	__asm__ __volatile__ (					\
 		"1:\n"						\
-		"	sw %z4, %2\n"				\
+		"	sw %z3, %1\n"				\
 		"2:\n"						\
-		"	sw %z5, %3\n"				\
+		"	sw %z4, %2\n"				\
 		"3:\n"						\
-		"	.section .fixup,\"ax\"\n"		\
-		"	.balign 4\n"				\
-		"4:\n"						\
-		"	li %0, %6\n"				\
-		"	jump 3b, %1\n"				\
-		"	.previous\n"				\
-			_ASM_EXTABLE(1b, 4b)			\
-			_ASM_EXTABLE(2b, 4b)			\
-		: "+r" (err), "=r" (__tmp),			\
+		_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %0)		\
+		_ASM_EXTABLE_UACCESS_ERR(2b, 3b, %0)		\
+		: "+r" (err),					\
 			"=m" (__ptr[__LSW]),			\
 			"=m" (__ptr[__MSW])			\
-		: "rJ" (__x), "rJ" (__x >> 32), "i" (-EFAULT));	\
+		: "rJ" (__x), "rJ" (__x >> 32));		\
 } while (0)
 #endif /* CONFIG_64BIT */
 
diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
index 91e52c4bb33a..05978f78579f 100644
--- a/arch/riscv/mm/extable.c
+++ b/arch/riscv/mm/extable.c
@@ -7,10 +7,12 @@
  */

+#include <linux/bitfield.h>
 #include <linux/extable.h>
 #include <linux/module.h>
 #include <linux/uaccess.h>
 #include <asm/asm-extable.h>
+#include <asm/ptrace.h>
 
 static inline unsigned long
 get_ex_fixup(const struct exception_table_entry *ex)
@@ -25,6 +27,29 @@ static bool ex_handler_fixup(const struct exception_table_entry *ex,
 	return true;
 }
 
+static inline void regs_set_gpr(struct pt_regs *regs, unsigned int offset,
+				unsigned long val)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return;
+
+	if (!offset)
+		*(unsigned long *)((unsigned long)regs + offset) = val;
+}
+
+static bool ex_handler_uaccess_err_zero(const struct exception_table_entry *ex,
+					struct pt_regs *regs)
+{
+	int reg_err = FIELD_GET(EX_DATA_REG_ERR, ex->data);
+	int reg_zero = FIELD_GET(EX_DATA_REG_ZERO, ex->data);
+
+	regs_set_gpr(regs, reg_err, -EFAULT);
+	regs_set_gpr(regs, reg_zero, 0);
+
+	regs->epc = get_ex_fixup(ex);
+	return true;
+}
+
 bool fixup_exception(struct pt_regs *regs)
 {
 	const struct exception_table_entry *ex;
@@ -38,6 +63,8 @@ bool fixup_exception(struct pt_regs *regs)
 		return ex_handler_fixup(ex, regs);
 	case EX_TYPE_BPF:
 		return ex_handler_bpf(ex, regs);
+	case EX_TYPE_UACCESS_ERR_ZERO:
+		return ex_handler_uaccess_err_zero(ex, regs);
 	}
 
 	BUG();
-- 
2.33.0