diff mbox series

[v4,8/9] powerpc/lib: Refactor __patch_instruction() to use __put_user_asm()

Message ID 20190228144917.16876-8-mpe@ellerman.id.au (mailing list archive)
State Superseded
Headers show
Series [v4,1/9] powerpc/powernv/idle: Restore IAMR after idle | expand

Checks

Context Check Description
snowpatch_ozlabs/apply_patch success next/apply_patch Successfully applied
snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 11 lines checked

Commit Message

Michael Ellerman Feb. 28, 2019, 2:49 p.m. UTC 
From: Russell Currey <ruscur@russell.cc>

__patch_instruction() is called in early boot, and uses
__put_user_size(), which includes the allow/prevent calls to enforce
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 <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/lib/code-patching.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

v4: Unchanged.
diff mbox series

Patch

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;