linux-kernel - [PATCH v4 1/9] x86/dumpstack: Remove unnecessary range check fetching opcode bytes

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Message-Id: <0a7892ea337e40d464ff291b264e40fbcd39f4af.1616004689.git.luto@kernel.org>
Date:   Wed, 17 Mar 2021 11:12:40 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Brian Gerst <brgerst@...il.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v4 1/9] x86/dumpstack: Remove unnecessary range check fetching opcode bytes

copy_from_user_nmi() validates that the pointer is in the user range,
so there is no need for an extra check in copy_code().

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/dumpstack.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 299c20f0a38b..55cf3c8325c6 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -81,12 +81,6 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
 	/* The user space code from other tasks cannot be accessed. */
 	if (regs != task_pt_regs(current))
 		return -EPERM;
-	/*
-	 * Make sure userspace isn't trying to trick us into dumping kernel
-	 * memory by pointing the userspace instruction pointer at it.
-	 */
-	if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX))
-		return -EINVAL;
 
 	/*
 	 * Even if named copy_from_user_nmi() this can be invoked from
-- 
2.30.2