Merge branch 'topic/user-access-begin' into next

Merge the user_access_begin() series from Christophe. This is based on
a commit from Linus that went into v5.5-rc7.

6 files changed, 219 insertions, 49 deletions

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index f9dc597b0b86..3c0ba22dc360 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -102,41 +102,91 @@ static inline void kuap_update_sr(u32 sr, u32 addr, u32 end)
 	isync();	/* Context sync required after mtsrin() */
 }
 
-static inline void allow_user_access(void __user *to, const void __user *from, u32 size)
+static __always_inline void allow_user_access(void __user *to, const void __user *from,
+					      u32 size, unsigned long dir)
 {
 	u32 addr, end;
 
-	if (__builtin_constant_p(to) && to == NULL)
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+	BUILD_BUG_ON(dir == KUAP_CURRENT);
+
+	if (!(dir & KUAP_WRITE))
 		return;
 
 	addr = (__force u32)to;
 
-	if (!addr || addr >= TASK_SIZE || !size)
+	if (unlikely(addr >= TASK_SIZE || !size))
 		return;
 
 	end = min(addr + size, TASK_SIZE);
+
 	current->thread.kuap = (addr & 0xf0000000) | ((((end - 1) >> 28) + 1) & 0xf);
 	kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end);	/* Clear Ks */
 }
 
-static inline void prevent_user_access(void __user *to, const void __user *from, u32 size)
+static __always_inline void prevent_user_access(void __user *to, const void __user *from,
+						u32 size, unsigned long dir)
 {
-	u32 addr = (__force u32)to;
-	u32 end = min(addr + size, TASK_SIZE);
+	u32 addr, end;
+
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+
+	if (dir == KUAP_CURRENT) {
+		u32 kuap = current->thread.kuap;
 
-	if (!addr || addr >= TASK_SIZE || !size)
+		if (unlikely(!kuap))
+			return;
+
+		addr = kuap & 0xf0000000;
+		end = kuap << 28;
+	} else if (dir & KUAP_WRITE) {
+		addr = (__force u32)to;
+		end = min(addr + size, TASK_SIZE);
+
+		if (unlikely(addr >= TASK_SIZE || !size))
+			return;
+	} else {
 		return;
+	}
 
 	current->thread.kuap = 0;
 	kuap_update_sr(mfsrin(addr) | SR_KS, addr, end);	/* set Ks */
 }
 
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write)
+static inline unsigned long prevent_user_access_return(void)
+{
+	unsigned long flags = current->thread.kuap;
+	unsigned long addr = flags & 0xf0000000;
+	unsigned long end = flags << 28;
+	void __user *to = (__force void __user *)addr;
+
+	if (flags)
+		prevent_user_access(to, to, end - addr, KUAP_READ_WRITE);
+
+	return flags;
+}
+
+static inline void restore_user_access(unsigned long flags)
 {
+	unsigned long addr = flags & 0xf0000000;
+	unsigned long end = flags << 28;
+	void __user *to = (__force void __user *)addr;
+
+	if (flags)
+		allow_user_access(to, to, end - addr, KUAP_READ_WRITE);
+}
+
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
+{
+	unsigned long begin = regs->kuap & 0xf0000000;
+	unsigned long end = regs->kuap << 28;
+
 	if (!is_write)
 		return false;
 
-	return WARN(!regs->kuap, "Bug: write fault blocked by segment registers !");
+	return WARN(address < begin || address >= end,
+		    "Bug: write fault blocked by segment registers !");
 }
 
 #endif /* CONFIG_PPC_KUAP */
diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h
index f254de956d6a..90dd3a3fc8c7 100644
--- a/arch/powerpc/include/asm/book3s/64/kup-radix.h
+++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h
@@ -63,6 +63,14 @@
  * because that would require an expensive read/modify write of the AMR.
  */
 
+static inline unsigned long get_kuap(void)
+{
+	if (!early_mmu_has_feature(MMU_FTR_RADIX_KUAP))
+		return 0;
+
+	return mfspr(SPRN_AMR);
+}
+
 static inline void set_kuap(unsigned long value)
 {
 	if (!early_mmu_has_feature(MMU_FTR_RADIX_KUAP))
@@ -77,25 +85,43 @@ static inline void set_kuap(unsigned long value)
 	isync();
 }
 
-static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size)
+static __always_inline void allow_user_access(void __user *to, const void __user *from,
+					      unsigned long size, unsigned long dir)
 {
 	// This is written so we can resolve to a single case at build time
-	if (__builtin_constant_p(to) && to == NULL)
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+	if (dir == KUAP_READ)
 		set_kuap(AMR_KUAP_BLOCK_WRITE);
-	else if (__builtin_constant_p(from) && from == NULL)
+	else if (dir == KUAP_WRITE)
 		set_kuap(AMR_KUAP_BLOCK_READ);
-	else
+	else if (dir == KUAP_READ_WRITE)
 		set_kuap(0);
+	else
+		BUILD_BUG();
 }
 
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size)
+				       unsigned long size, unsigned long dir)
+{
+	set_kuap(AMR_KUAP_BLOCKED);
+}
+
+static inline unsigned long prevent_user_access_return(void)
 {
+	unsigned long flags = get_kuap();
+
 	set_kuap(AMR_KUAP_BLOCKED);
+
+	return flags;
+}
+
+static inline void restore_user_access(unsigned long flags)
+{
+	set_kuap(flags);
 }
 
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write)
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 {
 	return WARN(mmu_has_feature(MMU_FTR_RADIX_KUAP) &&
 		    (regs->kuap & (is_write ? AMR_KUAP_BLOCK_WRITE : AMR_KUAP_BLOCK_READ)),
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 5b5e39643a27..92bcd1a26d73 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -2,6 +2,16 @@
 #ifndef _ASM_POWERPC_KUP_H_
 #define _ASM_POWERPC_KUP_H_
 
+#define KUAP_READ	1
+#define KUAP_WRITE	2
+#define KUAP_READ_WRITE	(KUAP_READ | KUAP_WRITE)
+/*
+ * For prevent_user_access() only.
+ * Use the current saved situation instead of the to/from/size params.
+ * Used on book3s/32
+ */
+#define KUAP_CURRENT	4
+
 #ifdef CONFIG_PPC64
 #include <asm/book3s/64/kup-radix.h>
 #endif
@@ -42,32 +52,55 @@ void setup_kuap(bool disabled);
 #else
 static inline void setup_kuap(bool disabled) { }
 static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size) { }
+				     unsigned long size, unsigned long dir) { }
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size) { }
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write) { return false; }
+				       unsigned long size, unsigned long dir) { }
+static inline unsigned long prevent_user_access_return(void) { return 0UL; }
+static inline void restore_user_access(unsigned long flags) { }
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
+{
+	return false;
+}
 #endif /* CONFIG_PPC_KUAP */
 
 static inline void allow_read_from_user(const void __user *from, unsigned long size)
 {
-	allow_user_access(NULL, from, size);
+	allow_user_access(NULL, from, size, KUAP_READ);
 }
 
 static inline void allow_write_to_user(void __user *to, unsigned long size)
 {
-	allow_user_access(to, NULL, size);
+	allow_user_access(to, NULL, size, KUAP_WRITE);
+}
+
+static inline void allow_read_write_user(void __user *to, const void __user *from,
+					 unsigned long size)
+{
+	allow_user_access(to, from, size, KUAP_READ_WRITE);
 }
 
 static inline void prevent_read_from_user(const void __user *from, unsigned long size)
 {
-	prevent_user_access(NULL, from, size);
+	prevent_user_access(NULL, from, size, KUAP_READ);
 }
 
 static inline void prevent_write_to_user(void __user *to, unsigned long size)
 {
-	prevent_user_access(to, NULL, size);
+	prevent_user_access(to, NULL, size, KUAP_WRITE);
+}
+
+static inline void prevent_read_write_user(void __user *to, const void __user *from,
+					   unsigned long size)
+{
+	prevent_user_access(to, from, size, KUAP_READ_WRITE);
+}
+
+static inline void prevent_current_access_user(void)
+{
+	prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT);
 }
 
 #endif /* !__ASSEMBLY__ */
 
-#endif /* _ASM_POWERPC_KUP_H_ */
+#endif /* _ASM_POWERPC_KUAP_H_ */
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 1006a427e99c..85ed2390fb99 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -35,18 +35,33 @@
 #include <asm/reg.h>
 
 static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size)
+				     unsigned long size, unsigned long dir)
 {
 	mtspr(SPRN_MD_AP, MD_APG_INIT);
 }
 
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size)
+				       unsigned long size, unsigned long dir)
 {
 	mtspr(SPRN_MD_AP, MD_APG_KUAP);
 }
 
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write)
+static inline unsigned long prevent_user_access_return(void)
+{
+	unsigned long flags = mfspr(SPRN_MD_AP);
+
+	mtspr(SPRN_MD_AP, MD_APG_KUAP);
+
+	return flags;
+}
+
+static inline void restore_user_access(unsigned long flags)
+{
+	mtspr(SPRN_MD_AP, flags);
+}
+
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 {
 	return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xf0000000),
 		    "Bug: fault blocked by AP register !");
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index c92fe7fe9692..2f500debae21 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -91,9 +91,14 @@ static inline int __access_ok(unsigned long addr, unsigned long size,
 	__put_user_check((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
 
 #define __get_user(x, ptr) \
-	__get_user_nocheck((x), (ptr), sizeof(*(ptr)))
+	__get_user_nocheck((x), (ptr), sizeof(*(ptr)), true)
 #define __put_user(x, ptr) \
-	__put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
+	__put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), true)
+
+#define __get_user_allowed(x, ptr) \
+	__get_user_nocheck((x), (ptr), sizeof(*(ptr)), false)
+#define __put_user_allowed(x, ptr) \
+	__put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), false)
 
 #define __get_user_inatomic(x, ptr) \
 	__get_user_nosleep((x), (ptr), sizeof(*(ptr)))
@@ -138,10 +143,9 @@ extern long __put_user_bad(void);
 		: "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
 #endif /* __powerpc64__ */
 
-#define __put_user_size(x, ptr, size, retval)			\
+#define __put_user_size_allowed(x, ptr, size, retval)		\
 do {								\
 	retval = 0;						\
-	allow_write_to_user(ptr, size);				\
 	switch (size) {						\
 	  case 1: __put_user_asm(x, ptr, retval, "stb"); break;	\
 	  case 2: __put_user_asm(x, ptr, retval, "sth"); break;	\
@@ -149,17 +153,26 @@ do {								\
 	  case 8: __put_user_asm2(x, ptr, retval); break;	\
 	  default: __put_user_bad();				\
 	}							\
+} while (0)
+
+#define __put_user_size(x, ptr, size, retval)			\
+do {								\
+	allow_write_to_user(ptr, size);				\
+	__put_user_size_allowed(x, ptr, size, retval);		\
 	prevent_write_to_user(ptr, size);			\
 } while (0)
 
-#define __put_user_nocheck(x, ptr, size)			\
+#define __put_user_nocheck(x, ptr, size, do_allow)			\
 ({								\
 	long __pu_err;						\
 	__typeof__(*(ptr)) __user *__pu_addr = (ptr);		\
 	if (!is_kernel_addr((unsigned long)__pu_addr))		\
 		might_fault();					\
 	__chk_user_ptr(ptr);					\
-	__put_user_size((x), __pu_addr, (size), __pu_err);	\
+	if (do_allow)								\
+		__put_user_size((x), __pu_addr, (size), __pu_err);		\
+	else									\
+		__put_user_size_allowed((x), __pu_addr, (size), __pu_err);	\
 	__pu_err;						\
 })
 
@@ -236,13 +249,12 @@ extern long __get_user_bad(void);
 		: "b" (addr), "i" (-EFAULT), "0" (err))
 #endif /* __powerpc64__ */
 
-#define __get_user_size(x, ptr, size, retval)			\
+#define __get_user_size_allowed(x, ptr, size, retval)		\
 do {								\
 	retval = 0;						\
 	__chk_user_ptr(ptr);					\
 	if (size > sizeof(x))					\
 		(x) = __get_user_bad();				\
-	allow_read_from_user(ptr, size);			\
 	switch (size) {						\
 	case 1: __get_user_asm(x, ptr, retval, "lbz"); break;	\
 	case 2: __get_user_asm(x, ptr, retval, "lhz"); break;	\
@@ -250,6 +262,12 @@ do {								\
 	case 8: __get_user_asm2(x, ptr, retval);  break;	\
 	default: (x) = __get_user_bad();			\
 	}							\
+} while (0)
+
+#define __get_user_size(x, ptr, size, retval)			\
+do {								\
+	allow_read_from_user(ptr, size);			\
+	__get_user_size_allowed(x, ptr, size, retval);		\
 	prevent_read_from_user(ptr, size);			\
 } while (0)
 
@@ -260,7 +278,7 @@ do {								\
 #define __long_type(x) \
 	__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 
-#define __get_user_nocheck(x, ptr, size)			\
+#define __get_user_nocheck(x, ptr, size, do_allow)			\
 ({								\
 	long __gu_err;						\
 	__long_type(*(ptr)) __gu_val;				\
@@ -269,7 +287,10 @@ do {								\
 	if (!is_kernel_addr((unsigned long)__gu_addr))		\
 		might_fault();					\
 	barrier_nospec();					\
-	__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
+	if (do_allow)								\
+		__get_user_size(__gu_val, __gu_addr, (size), __gu_err);		\
+	else									\
+		__get_user_size_allowed(__gu_val, __gu_addr, (size), __gu_err);	\
 	(x) = (__typeof__(*(ptr)))__gu_val;			\
 	__gu_err;						\
 })
@@ -313,9 +334,9 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 	unsigned long ret;
 
 	barrier_nospec();
-	allow_user_access(to, from, n);
+	allow_read_write_user(to, from, n);
 	ret = __copy_tofrom_user(to, from, n);
-	prevent_user_access(to, from, n);
+	prevent_read_write_user(to, from, n);
 	return ret;
 }
 #endif /* __powerpc64__ */
@@ -356,33 +377,40 @@ static inline unsigned long raw_copy_from_user(void *to,
 	return ret;
 }
 
-static inline unsigned long raw_copy_to_user(void __user *to,
-		const void *from, unsigned long n)
+static inline unsigned long
+raw_copy_to_user_allowed(void __user *to, const void *from, unsigned long n)
 {
-	unsigned long ret;
 	if (__builtin_constant_p(n) && (n <= 8)) {
-		ret = 1;
+		unsigned long ret = 1;
 
 		switch (n) {
 		case 1:
-			__put_user_size(*(u8 *)from, (u8 __user *)to, 1, ret);
+			__put_user_size_allowed(*(u8 *)from, (u8 __user *)to, 1, ret);
 			break;
 		case 2:
-			__put_user_size(*(u16 *)from, (u16 __user *)to, 2, ret);
+			__put_user_size_allowed(*(u16 *)from, (u16 __user *)to, 2, ret);
 			break;
 		case 4:
-			__put_user_size(*(u32 *)from, (u32 __user *)to, 4, ret);
+			__put_user_size_allowed(*(u32 *)from, (u32 __user *)to, 4, ret);
 			break;
 		case 8:
-			__put_user_size(*(u64 *)from, (u64 __user *)to, 8, ret);
+			__put_user_size_allowed(*(u64 *)from, (u64 __user *)to, 8, ret);
 			break;
 		}
 		if (ret == 0)
 			return 0;
 	}
 
+	return __copy_tofrom_user(to, (__force const void __user *)from, n);
+}
+
+static inline unsigned long
+raw_copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	unsigned long ret;
+
 	allow_write_to_user(to, n);
-	ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
+	ret = raw_copy_to_user_allowed(to, from, n);
 	prevent_write_to_user(to, n);
 	return ret;
 }
@@ -428,4 +456,22 @@ extern long __copy_from_user_flushcache(void *dst, const void __user *src,
 extern void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
 			   size_t len);
 
+static __must_check inline bool user_access_begin(const void __user *ptr, size_t len)
+{
+	if (unlikely(!access_ok(ptr, len)))
+		return false;
+	allow_read_write_user((void __user *)ptr, ptr, len);
+	return true;
+}
+#define user_access_begin	user_access_begin
+#define user_access_end		prevent_current_access_user
+#define user_access_save	prevent_user_access_return
+#define user_access_restore	restore_user_access
+
+#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
+#define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
+#define unsafe_put_user(x, p, e) unsafe_op_wrap(__put_user_allowed(x, p), e)
+#define unsafe_copy_to_user(d, s, l, e) \
+	unsafe_op_wrap(raw_copy_to_user_allowed(d, s, l), e)
+
 #endif	/* _ARCH_POWERPC_UACCESS_H */
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 7534ee5bf9b2..8db0507619e2 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -233,7 +233,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
 
 	// Read/write fault in a valid region (the exception table search passed
 	// above), but blocked by KUAP is bad, it can never succeed.
-	if (bad_kuap_fault(regs, is_write))
+	if (bad_kuap_fault(regs, address, is_write))
 		return true;
 
 	// What's left? Kernel fault on user in well defined regions (extable