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

From: Josh Poimboeuf
Date: Thu Jul 25 2019 - 16:30:47 EST


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@xxxxxxxxxxxxx>
Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
.../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