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From: Russell Currey <>
	Russell Currey <>
Subject: [PATCH 6/7] powerpc/lib: Refactor __patch_instruction() to use __put_user_asm()
Date: Thu, 21 Feb 2019 20:36:00 +1100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

__patch_instruction() is called in early boot, and uses
__put_user_size(), which includes the locks and unlocks for KUAP,
which could either be called too early, or in the Radix case, forced to
use "early_" versions of functions just to safely handle this one case.

__put_user_asm() does not do this, and thus is safe to use both in early
boot, and later on since in this case it should only ever be touching
kernel memory.

__patch_instruction() was previously refactored to use __put_user_size()
in order to be able to return -EFAULT, which would allow the kernel to
patch instructions in userspace, which should never happen.  This has
the functional change of causing faults on userspace addresses if KUAP
is turned on, which should never happen in practice.

A future enhancement could be to double check the patch address is
definitely allowed to be tampered with by the kernel.

Signed-off-by: Russell Currey <>
 arch/powerpc/lib/code-patching.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 506413a2c25e..42fdadac6587 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -26,9 +26,9 @@
 static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
 			       unsigned int *patch_addr)
-	int err;
+	int err = 0;
-	__put_user_size(instr, patch_addr, 4, err);
+	__put_user_asm(instr, patch_addr, err, "stw");
 	if (err)
 		return err;

  parent reply	other threads:[~2019-02-21  9:36 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-21  9:35 [PATCH 0/7] Kernel Userspace Protection for radix Russell Currey
2019-02-21  9:35 ` [PATCH 1/7] powerpc: Add framework for Kernel Userspace Protection Russell Currey
2019-02-21  9:35 ` [PATCH 2/7] powerpc: Add skeleton for Kernel Userspace Execution Prevention Russell Currey
2019-02-21  9:35 ` [PATCH 3/7] powerpc/mm: Add a framework for Kernel Userspace Access Protection Russell Currey
2019-02-21 10:46   ` Christophe Leroy
2019-02-21 14:48     ` Mark Rutland
2019-02-22  0:11       ` Russell Currey
2019-02-21 12:56   ` kbuild test robot
2019-02-21  9:35 ` [PATCH 4/7] powerpc/64: Setup KUP on secondary CPUs Russell Currey
2019-02-21  9:35 ` [PATCH 5/7] powerpc/mm/radix: Use KUEP API for Radix MMU Russell Currey
2019-02-21  9:36 ` Russell Currey [this message]
2019-02-21  9:36 ` [PATCH 7/7] powerpc/64s: Implement KUAP " Russell Currey
2019-02-22  5:14   ` Nicholas Piggin
2019-02-21 16:07 ` [PATCH 0/7] Kernel Userspace Protection for radix Kees Cook
2019-02-22  0:09   ` Russell Currey
2019-02-22  0:16     ` Kees Cook
2019-02-22  3:46       ` Michael Ellerman

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