linux-kernel - [PATCH 3.16 164/204] arm64: ensure __dump_instr() checks addr

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Message-ID: <lsq.1514480744.65680997@decadent.org.uk>
Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        "Will Deacon" <will.deacon@....com>
Subject: [PATCH 3.16 164/204] arm64: ensure __dump_instr() checks addr_limit

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Rutland <mark.rutland@....com>

commit 7a7003b1da010d2b0d1dc8bf21c10f5c73b389f1 upstream.

It's possible for a user to deliberately trigger __dump_instr with a
chosen kernel address.

Let's avoid problems resulting from this by using get_user() rather than
__get_user(), ensuring that we don't erroneously access kernel memory.

Where we use __dump_instr() on kernel text, we already switch to
KERNEL_DS, so this shouldn't adversely affect those cases.

Fixes: 60ffc30d5652810d ("arm64: Exception handling")
Acked-by: Will Deacon <will.deacon@....com>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm64/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -105,7 +105,7 @@ static void __dump_instr(const char *lvl
 	for (i = -4; i < 1; i++) {
 		unsigned int val, bad;
 
-		bad = __get_user(val, &((u32 *)addr)[i]);
+		bad = get_user(val, &((u32 *)addr)[i]);
 
 		if (!bad)
 			p += sprintf(p, i == 0 ? "(%08x) " : "%08x ", val);