[PATCH] drm/i915: Remove redundant user_access_end() from __copy_from_user() error path - dri-devel - freedesktop.org experimental mailing list

25 Jul 2019

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@linutronix.de
Reported-by: Sedat Dilek sedat.dilek@gmail.com
Acked-by: Peter Zijlstra (Intel) peterz@infradead.org
Tested-by: Nick Desaulniers ndesaulniers@google.com
Tested-by: Sedat Dilek sedat.dilek@gmail.com
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com
---
 .../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 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
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);
    }
-- 
2.20.1


    