Subject: [PATCH] arm: fix page faults in do_alignment

From: Jing Xiangfeng <[email-masked]>
Date: Fri, 30 Aug 2019 21:31:17 +0800

The function do_alignment can handle misaligned address for user and
kernel space. If it is a userspace access, do_alignment may fail on
a low-memory situation, because page faults are disabled in
probe_kernel_address.

Fix this by using __copy_from_user stead of probe_kernel_address.

Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code")
Signed-off-by: Jing Xiangfeng <[email-masked]>
---
 arch/arm/mm/alignment.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index 04b3643..2ccabd3 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -774,6 +774,7 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
 	unsigned long instr = 0, instrptr;
 	int (*handler)(unsigned long addr, unsigned long instr, struct pt_regs *regs);
 	unsigned int type;
+	mm_segment_t fs;
 	unsigned int fault;
 	u16 tinstr = 0;
 	int isize = 4;
@@ -784,16 +785,22 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
 
 	instrptr = instruction_pointer(regs);
 
+	fs = get_fs();
+	set_fs(KERNEL_DS);
 	if (thumb_mode(regs)) {
 		u16 *ptr = (u16 *)(instrptr & ~1);
-		fault = probe_kernel_address(ptr, tinstr);
+		fault = __copy_from_user(tinstr,
+				(__force const void __user *)ptr,
+				sizeof(tinstr));
 		tinstr = __mem_to_opcode_thumb16(tinstr);
 		if (!fault) {
 			if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
 			    IS_T32(tinstr)) {
 				/* Thumb-2 32-bit */
 				u16 tinst2 = 0;
-				fault = probe_kernel_address(ptr + 1, tinst2);
+				fault = __copy_from_user(tinst2,
+						(__force const void __user *)(ptr+1),
+						sizeof(tinst2));
 				tinst2 = __mem_to_opcode_thumb16(tinst2);
 				instr = __opcode_thumb32_compose(tinstr, tinst2);
 				thumb2_32b = 1;
@@ -803,10 +810,13 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
 			}
 		}
 	} else {
-		fault = probe_kernel_address((void *)instrptr, instr);
+		fault = __copy_from_user(instr,
+				(__force const void __user *)instrptr,
+				sizeof(instr));
 		instr = __mem_to_opcode_arm(instr);
 	}
 
+	set_fs(fs);
 	if (fault) {
 		type = TYPE_FAULT;
 		goto bad_or_fault;
-- 
1.8.3.1

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