* Borislav Petkov <[email protected]> wrote:
> From: Borislav Petkov <[email protected]>
>
> Use the asm macro and drop the locally grown version.
> @@ -73,9 +49,11 @@ ENTRY(_copy_to_user)
> jc bad_to_user
> cmpq TI_addr_limit(%rax),%rcx
> ja bad_to_user
> + ALTERNATIVE_2 "jmp copy_user_generic_unrolled", \
> + "jmp copy_user_generic_string", \
> + X86_FEATURE_REP_GOOD, \
> + "jmp copy_user_enhanced_fast_string", \
> + X86_FEATURE_ERMS
Btw., as a future optimization, wouldn't it be useful to patch this
function at its first instruction, i.e. to have three fully functional
copy_user_generic_ variants and choose to jmp to one of them in the
first instruction of the original function?
The advantage would be two-fold:
1) right now: smart microarchitectures that are able to optimize
jump-after-jump (and jump-after-call) targets in their branch
target cache can do so in this case, reducing the overhead of the
patching, possibly close to zero in the cached case.
2) in the future: we could actually do a (limited) re-link of the
kernel during bootup, and patch up the original copy_to_user call
sites directly to one of the three variants. Alternatives patching
done at the symbol level. Does current tooling allow something
like this already?
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
