diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2024-10-29 16:03:31 -1000 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2024-10-30 11:38:10 -1000 |
| commit | 0fc810ae3ae110f9e2fcccce80fc8c8d62f97907 (patch) | |
| tree | 983d3b661ca5c20363d7066b01252b6473ee95a3 /include | |
| parent | 14b7d43c5c068cb9688a9fe68883f4340effb053 (diff) | |
x86/uaccess: Avoid barrier_nospec() in 64-bit copy_from_user()
The barrier_nospec() in 64-bit copy_from_user() is slow. Instead use
pointer masking to force the user pointer to all 1's for an invalid
address.
The kernel test robot reports a 2.6% improvement in the per_thread_ops
benchmark [1].
This is a variation on a patch originally by Josh Poimboeuf [2].
Link: https://lore.kernel.org/202410281344.d02c72a2-oliver.sang@intel.com [1]
Link: https://lore.kernel.org/5b887fe4c580214900e21f6c61095adf9a142735.1730166635.git.jpoimboe@kernel.org [2]
Tested-and-reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/uaccess.h | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 39c7cf82b0c2..43844510d5d0 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -38,6 +38,7 @@ #else #define can_do_masked_user_access() 0 #define masked_user_access_begin(src) NULL + #define mask_user_address(src) (src) #endif /* @@ -159,19 +160,27 @@ _inline_copy_from_user(void *to, const void __user *from, unsigned long n) { unsigned long res = n; might_fault(); - if (!should_fail_usercopy() && likely(access_ok(from, n))) { + if (should_fail_usercopy()) + goto fail; + if (can_do_masked_user_access()) + from = mask_user_address(from); + else { + if (!access_ok(from, n)) + goto fail; /* * Ensure that bad access_ok() speculation will not * lead to nasty side effects *after* the copy is * finished: */ barrier_nospec(); - instrument_copy_from_user_before(to, from, n); - res = raw_copy_from_user(to, from, n); - instrument_copy_from_user_after(to, from, n, res); } - if (unlikely(res)) - memset(to + (n - res), 0, res); + instrument_copy_from_user_before(to, from, n); + res = raw_copy_from_user(to, from, n); + instrument_copy_from_user_after(to, from, n, res); + if (likely(!res)) + return 0; +fail: + memset(to + (n - res), 0, res); return res; } extern __must_check unsigned long |