Some architectures like powerpc64 have the capability to separate
read access and write access protection.
For get_user() and copy_from_user(), powerpc64 only open read access.
For put_user() and copy_to_user(), powerpc64 only open write access.
But when using unsafe_get_user() or unsafe_put_user(),
user_access_begin open both read and write.
In order to avoid any risk based of hacking some variable parameters
passed to user_access_begin/end that would allow hacking and
leaving user access open or opening too much, it is preferable to
use dedicated static functions that can't be overridden.
Add a user_read_access_begin and user_read_access_end to only open
read access.
Add a user_write_access_begin and user_write_access_end to only open
write access.
By default, when undefined, those new access helpers default on the
existing user_access_begin and user_access_end.
Signed-off-by: Christophe Leroy <[email protected]>
---
include/linux/uaccess.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 67f016010aad..9861c89f93be 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -378,6 +378,14 @@ extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count);
static inline unsigned long user_access_save(void) { return 0UL; }
static inline void user_access_restore(unsigned long flags) { }
#endif
+#ifndef user_write_access_begin
+#define user_write_access_begin user_access_begin
+#define user_write_access_end user_access_end
+#endif
+#ifndef user_read_access_begin
+#define user_read_access_begin user_access_begin
+#define user_read_access_end user_access_end
+#endif
#ifdef CONFIG_HARDENED_USERCOPY
void usercopy_warn(const char *name, const char *detail, bool to_user,
--
2.25.0
When i915_gem_execbuffer2_ioctl() is using user_access_begin(),
that's only to perform unsafe_put_user() so use
user_write_access_begin() in order to only open write access.
Signed-off-by: Christophe Leroy <[email protected]>
---
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index d5a0f5ae4a8b..f8ebd54fe69c 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1610,14 +1610,14 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
* happened we would make the mistake of assuming that the
* relocations were valid.
*/
- if (!user_access_begin(urelocs, size))
+ if (!user_write_access_begin(urelocs, size))
goto end;
for (copied = 0; copied < nreloc; copied++)
unsafe_put_user(-1,
&urelocs[copied].presumed_offset,
end_user);
- user_access_end();
+ user_write_access_end();
eb->exec[i].relocs_ptr = (uintptr_t)relocs;
}
@@ -1625,7 +1625,7 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
return 0;
end_user:
- user_access_end();
+ user_write_access_end();
end:
kvfree(relocs);
err = -EFAULT;
@@ -2955,7 +2955,8 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
* And this range already got effectively checked earlier
* when we did the "copy_from_user()" above.
*/
- if (!user_access_begin(user_exec_list, count * sizeof(*user_exec_list)))
+ if (!user_write_access_begin(user_exec_list,
+ count * sizeof(*user_exec_list)))
goto end;
for (i = 0; i < args->buffer_count; i++) {
@@ -2969,7 +2970,7 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
end_user);
}
end_user:
- user_access_end();
+ user_write_access_end();
end:;
}
--
2.25.0