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From:   Christoph Hellwig <hch@lst.de>
To:     nickhu@andestech.com, green.hu@gmail.com, deanbo422@gmail.com
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] nds32: use get_kernel_nofault in dump_mem
Date:   Mon, 20 Jul 2020 13:44:48 +0200
Message-Id: <20200720114448.205876-2-hch@lst.de>
In-Reply-To: <20200720114448.205876-1-hch@lst.de>
References: <20200720114448.205876-1-hch@lst.de>
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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/nds32/kernel/traps.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/nds32/kernel/traps.c b/arch/nds32/kernel/traps.c
index b66f889bc6df9b..ee0d9ae192a504 100644
--- a/arch/nds32/kernel/traps.c
+++ b/arch/nds32/kernel/traps.c
@@ -25,17 +25,8 @@ extern void show_pte(struct mm_struct *mm, unsigned long addr);
 void dump_mem(const char *lvl, 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);
-
 	pr_emerg("%s(0x%08lx to 0x%08lx)\n", lvl, bottom, top);
 
 	for (first = bottom & ~31; first < top; first += 32) {
@@ -48,7 +39,9 @@ void dump_mem(const char *lvl, unsigned long bottom, unsigned long top)
 		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, " ????????");
@@ -56,8 +49,6 @@ void dump_mem(const char *lvl, unsigned long bottom, unsigned long top)
 		}
 		pr_emerg("%s%04lx:%s\n", lvl, first & 0xffff, str);
 	}
-
-	set_fs(fs);
 }
 
 EXPORT_SYMBOL(dump_mem);
-- 
2.27.0