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SubjectRe: x86 - clang / objtool status
On Thu, Jul 18, 2019 at 10:40:09PM +0200, Thomas Gleixner wrote:

> drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x86: redundant UACCESS disable

Looking at this one, I think I agree with objtool.

PeterZ, Linus, I know y'all discussed this code a few months ago.

__copy_from_user() already does a CLAC in its error path. So isn't the
user_access_end() redundant for the __copy_from_user() error path?

Untested fix:

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);
}
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