linux-kernel - [tip:core/urgent] drm/i915: Remove redundant user_access_end() from __copy_from

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Message-ID: <tip-e6a9522ac3ff59980ea00e070b6b8573aface36a@git.kernel.org>
Date:   Fri, 9 Aug 2019 14:16:21 -0700
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        tglx@...utronix.de, sedat.dilek@...il.com, hpa@...or.com,
        peterz@...radead.org, mingo@...nel.org, chris@...is-wilson.co.uk,
        jpoimboe@...hat.com
Subject: [tip:core/urgent] drm/i915: Remove redundant user_access_end() from
 __copy_from_user() error path

Commit-ID:  e6a9522ac3ff59980ea00e070b6b8573aface36a
Gitweb:     https://git.kernel.org/tip/e6a9522ac3ff59980ea00e070b6b8573aface36a
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Thu, 25 Jul 2019 15:29:57 -0500
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 9 Aug 2019 23:13:25 +0200

drm/i915: Remove redundant user_access_end() from __copy_from_user() error path

Objtool reports:

  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x36: redundant UACCESS disable

__copy_from_user() already does both STAC and CLAC, so the
user_access_end() in its error path adds an extra unnecessary CLAC.

Fixes: 0b2c8f8b6b0c ("i915: fix missing user_access_end() in page fault exception case")
Reported-by: Thomas Gleixner <tglx@...utronix.de>
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Chris Wilson <chris@...is-wilson.co.uk>
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Link: https://lkml.kernel.org/r/51a4155c5bc2ca847a9cbe85c1c11918bb193141.1564086017.git.jpoimboe@redhat.com

---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 5fae0e50aad0..41dab9ea33cd 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1628,6 +1628,7 @@ static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
 
 static int eb_copy_relocations(const struct i915_execbuffer *eb)
 {
+	struct drm_i915_gem_relocation_entry *relocs;
 	const unsigned int count = eb->buffer_count;
 	unsigned int i;
 	int err;
@@ -1635,7 +1636,6 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 	for (i = 0; i < count; i++) {
 		const unsigned int nreloc = eb->exec[i].relocation_count;
 		struct drm_i915_gem_relocation_entry __user *urelocs;
-		struct drm_i915_gem_relocation_entry *relocs;
 		unsigned long size;
 		unsigned long copied;
 
@@ -1663,14 +1663,8 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 
 			if (__copy_from_user((char *)relocs + copied,
 					     (char __user *)urelocs + copied,
-					     len)) {
-end_user:
-				user_access_end();
-end:
-				kvfree(relocs);
-				err = -EFAULT;
-				goto err;
-			}
+					     len))
+				goto end;
 
 			copied += len;
 		} while (copied < size);
@@ -1699,10 +1693,14 @@ end:
 
 	return 0;
 
+end_user:
+	user_access_end();
+end:
+	kvfree(relocs);
+	err = -EFAULT;
 err:
 	while (i--) {
-		struct drm_i915_gem_relocation_entry *relocs =
-			u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
+		relocs = u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
 		if (eb->exec[i].relocation_count)
 			kvfree(relocs);
 	}