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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Anvin <hpa@zytor.com>,
	Ingo Molnar <mingo@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-arch <linux-arch@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5/7] arm64: start using 'asm goto' for get_user() when available
Date: Mon, 10 Jun 2024 13:48:19 -0700
Message-ID: <20240610204821.230388-6-torvalds@linux-foundation.org>
In-Reply-To: <20240610204821.230388-1-torvalds@linux-foundation.org>
References: <20240610204821.230388-1-torvalds@linux-foundation.org>
Precedence: bulk
MIME-Version: 1.0
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This generates noticeably better code with compilers that support it,
since we don't need to test the error register etc, the exception just
jumps to the error handling directly.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/arm64/include/asm/uaccess.h | 113 ++++++++++++++++++++++++-------
 arch/arm64/kernel/mte.c          |  12 ++--
 2 files changed, 95 insertions(+), 30 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 14be5000c5a0..23c2edf517ed 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -184,29 +184,40 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
  * The "__xxx_error" versions set the third argument to -EFAULT if an error
  * occurs, and leave it unchanged on success.
  */
-#define __get_mem_asm(load, reg, x, addr, err, type)			\
+#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
+#define __get_mem_asm(load, reg, x, addr, label, type)			\
+	asm_goto_output(						\
+	"1:	" load "	" reg "0, [%1]\n"			\
+	_ASM_EXTABLE_##type##ACCESS_ERR(1b, %l2, %w0)			\
+	: "=r" (x)							\
+	: "r" (addr) : : label)
+#else
+#define __get_mem_asm(load, reg, x, addr, label, type) do {		\
+	int __gma_err = 0;						\
 	asm volatile(							\
 	"1:	" load "	" reg "1, [%2]\n"			\
 	"2:\n"								\
 	_ASM_EXTABLE_##type##ACCESS_ERR_ZERO(1b, 2b, %w0, %w1)		\
-	: "+r" (err), "=r" (x)						\
-	: "r" (addr))
+	: "+r" (__gma_err), "=r" (x)					\
+	: "r" (addr));							\
+	if (__gma_err) goto label; } while (0)
+#endif
 
-#define __raw_get_mem(ldr, x, ptr, err, type)					\
+#define __raw_get_mem(ldr, x, ptr, label, type)					\
 do {										\
 	unsigned long __gu_val;							\
 	switch (sizeof(*(ptr))) {						\
 	case 1:									\
-		__get_mem_asm(ldr "b", "%w", __gu_val, (ptr), (err), type);	\
+		__get_mem_asm(ldr "b", "%w", __gu_val, (ptr), label, type);	\
 		break;								\
 	case 2:									\
-		__get_mem_asm(ldr "h", "%w", __gu_val, (ptr), (err), type);	\
+		__get_mem_asm(ldr "h", "%w", __gu_val, (ptr), label, type);	\
 		break;								\
 	case 4:									\
-		__get_mem_asm(ldr, "%w", __gu_val, (ptr), (err), type);		\
+		__get_mem_asm(ldr, "%w", __gu_val, (ptr), label, type);		\
 		break;								\
 	case 8:									\
-		__get_mem_asm(ldr, "%x",  __gu_val, (ptr), (err), type);	\
+		__get_mem_asm(ldr, "%x",  __gu_val, (ptr), label, type);	\
 		break;								\
 	default:								\
 		BUILD_BUG();							\
@@ -219,27 +230,34 @@ do {										\
  * uaccess_ttbr0_disable(). As `x` and `ptr` could contain blocking functions,
  * we must evaluate these outside of the critical section.
  */
-#define __raw_get_user(x, ptr, err)					\
+#define __raw_get_user(x, ptr, label)					\
 do {									\
 	__typeof__(*(ptr)) __user *__rgu_ptr = (ptr);			\
 	__typeof__(x) __rgu_val;					\
 	__chk_user_ptr(ptr);						\
-									\
-	uaccess_ttbr0_enable();						\
-	__raw_get_mem("ldtr", __rgu_val, __rgu_ptr, err, U);		\
-	uaccess_ttbr0_disable();					\
-									\
-	(x) = __rgu_val;						\
+	do {								\
+		__label__ __rgu_failed;					\
+		uaccess_ttbr0_enable();					\
+		__raw_get_mem("ldtr", __rgu_val, __rgu_ptr, __rgu_failed, U);	\
+		uaccess_ttbr0_disable();				\
+		(x) = __rgu_val;					\
+		break;							\
+	__rgu_failed:							\
+		uaccess_ttbr0_disable();				\
+		goto label;						\
+	} while (0);							\
 } while (0)
 
 #define __get_user_error(x, ptr, err)					\
 do {									\
+	__label__ __gu_failed;						\
 	__typeof__(*(ptr)) __user *__p = (ptr);				\
 	might_fault();							\
 	if (access_ok(__p, sizeof(*__p))) {				\
 		__p = uaccess_mask_ptr(__p);				\
-		__raw_get_user((x), __p, (err));			\
+		__raw_get_user((x), __p, __gu_failed);			\
 	} else {							\
+	__gu_failed:							\
 		(x) = (__force __typeof__(x))0; (err) = -EFAULT;	\
 	}								\
 } while (0)
@@ -262,15 +280,18 @@ do {									\
 do {									\
 	__typeof__(dst) __gkn_dst = (dst);				\
 	__typeof__(src) __gkn_src = (src);				\
-	int __gkn_err = 0;						\
+	do { 								\
+		__label__ __gkn_label;					\
 									\
-	__mte_enable_tco_async();					\
-	__raw_get_mem("ldr", *((type *)(__gkn_dst)),			\
-		      (__force type *)(__gkn_src), __gkn_err, K);	\
-	__mte_disable_tco_async();					\
-									\
-	if (unlikely(__gkn_err))					\
+		__mte_enable_tco_async();				\
+		__raw_get_mem("ldr", *((type *)(__gkn_dst)),		\
+		      (__force type *)(__gkn_src), __gkn_label, K);	\
+		__mte_disable_tco_async();				\
+		break;							\
+	__gkn_label:							\
+		__mte_disable_tco_async();				\
 		goto err_label;						\
+	} while (0);							\
 } while (0)
 
 #define __put_mem_asm(store, reg, x, addr, err, type)			\
@@ -381,6 +402,52 @@ extern unsigned long __must_check __arch_copy_to_user(void __user *to, const voi
 	__actu_ret;							\
 })
 
+static __must_check __always_inline bool user_access_begin(const void __user *ptr, size_t len)
+{
+	if (unlikely(!access_ok(ptr,len)))
+		return 0;
+	uaccess_ttbr0_enable();
+	return 1;
+}
+#define user_access_begin(a,b)	user_access_begin(a,b)
+#define user_access_end()	uaccess_ttbr0_disable()
+
+/*
+ * The arm64 inline asms should learn abut asm goto, and we should
+ * teach user_access_begin() about address masking.
+ */
+#define unsafe_put_user(x, ptr, label)	do {				\
+	int __upu_err = 0;						\
+	__raw_put_mem("sttr", x, uaccess_mask_ptr(ptr), __upu_err, U);	\
+	if (__upu_err) goto label;				\
+} while (0)
+
+#define unsafe_get_user(x, ptr, label) \
+	__raw_get_mem("ldtr", x, uaccess_mask_ptr(ptr), label, U)
+
+/*
+ * We want the unsafe accessors to always be inlined and use
+ * the error labels - thus the macro games.
+ */
+#define unsafe_copy_loop(dst, src, len, type, label)				\
+	while (len >= sizeof(type)) {						\
+		unsafe_put_user(*(type *)(src),(type __user *)(dst),label);	\
+		dst += sizeof(type);						\
+		src += sizeof(type);						\
+		len -= sizeof(type);						\
+	}
+
+#define unsafe_copy_to_user(_dst,_src,_len,label)			\
+do {									\
+	char __user *__ucu_dst = (_dst);				\
+	const char *__ucu_src = (_src);					\
+	size_t __ucu_len = (_len);					\
+	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
+	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
+	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
+	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
+} while (0)
+
 #define INLINE_COPY_TO_USER
 #define INLINE_COPY_FROM_USER
 
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index dcdcccd40891..6174671be7c1 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -582,12 +582,9 @@ subsys_initcall(register_mte_tcf_preferred_sysctl);
 size_t mte_probe_user_range(const char __user *uaddr, size_t size)
 {
 	const char __user *end = uaddr + size;
-	int err = 0;
 	char val;
 
-	__raw_get_user(val, uaddr, err);
-	if (err)
-		return size;
+	__raw_get_user(val, uaddr, efault);
 
 	uaddr = PTR_ALIGN(uaddr, MTE_GRANULE_SIZE);
 	while (uaddr < end) {
@@ -595,12 +592,13 @@ size_t mte_probe_user_range(const char __user *uaddr, size_t size)
 		 * A read is sufficient for mte, the caller should have probed
 		 * for the pte write permission if required.
 		 */
-		__raw_get_user(val, uaddr, err);
-		if (err)
-			return end - uaddr;
+		__raw_get_user(val, uaddr, efault);
 		uaddr += MTE_GRANULE_SIZE;
 	}
 	(void)val;
 
 	return 0;
+
+efault:
+	return end - uaddr;
 }
-- 
2.45.1.209.gc6f12300df