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From:   Christoph Hellwig <hch@lst.de>
To:     gxt@pku.edu.cn
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] unicore32: use get_kernel_nofault in dump mem and dump_instr
Date:   Mon, 20 Jul 2020 13:43:58 +0200
Message-Id: <20200720114358.201161-1-hch@lst.de>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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Use the proper get_kernel_nofault helper to access an unsafe kernel
pointer without faulting instead of playing with set_fs and get_user.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/unicore32/kernel/traps.c | 28 +++-------------------------
 1 file changed, 3 insertions(+), 25 deletions(-)

diff --git a/arch/unicore32/kernel/traps.c b/arch/unicore32/kernel/traps.c
index a3ac01df1a2e43..c1964a4a1edbb0 100644
--- a/arch/unicore32/kernel/traps.c
+++ b/arch/unicore32/kernel/traps.c
@@ -65,17 +65,8 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
 		     unsigned long top)
 {
 	unsigned long first;
-	mm_segment_t fs;
 	int i;
 
-	/*
-	 * We need to switch to kernel mode so that we can use __get_user
-	 * to safely read from kernel space.  Note that we now dump the
-	 * code first, just in case the backtrace kills us.
-	 */
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-
 	printk(KERN_DEFAULT "%s%s(0x%08lx to 0x%08lx)\n",
 			lvl, str, bottom, top);
 
@@ -89,7 +80,8 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
 		for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
 			if (p >= bottom && p < top) {
 				unsigned long val;
-				if (__get_user(val, (unsigned long *)p) == 0)
+				if (get_kernel_nofault(val, (unsigned long *)p)
+						== 0)
 					sprintf(str + i * 9, " %08lx", val);
 				else
 					sprintf(str + i * 9, " ????????");
@@ -97,31 +89,19 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
 		}
 		printk(KERN_DEFAULT "%s%04lx:%s\n", lvl, first & 0xffff, str);
 	}
-
-	set_fs(fs);
 }
 
 static void dump_instr(const char *lvl, struct pt_regs *regs)
 {
 	unsigned long addr = instruction_pointer(regs);
 	const int width = 8;
-	mm_segment_t fs;
 	char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
 	int i;
 
-	/*
-	 * We need to switch to kernel mode so that we can use __get_user
-	 * to safely read from kernel space.  Note that we now dump the
-	 * code first, just in case the backtrace kills us.
-	 */
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-
 	for (i = -4; i < 1; i++) {
 		unsigned int val, bad;
 
-		bad = __get_user(val, &((u32 *)addr)[i]);
-
+		bad = get_kernel_nofault(val, &((u32 *)addr)[i]);
 		if (!bad)
 			p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ",
 					width, val);
@@ -131,8 +111,6 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
 		}
 	}
 	printk(KERN_DEFAULT "%sCode: %s\n", lvl, str);
-
-	set_fs(fs);
 }
 
 static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
-- 
2.27.0