[PATCH 0/6] x86/alternatives: text_poke() fixes

From: Nadav Amit
Date: Thu Aug 30 2018 - 13:34:35 EST

This patch-set addresses some issues that were raised in a recent
correspondence and might affect the security and the correctness of code
patching. (Note that patching performance is not addressed by this

The main issue that the patches deal with is the fact that the fixmap
PTEs that are used for patching are available for access from other
cores and might be exploited. They are not even flushed from the TLB in
remote cores, so the risk is even higher. Address this issue by
introducing a temporary mm that is only used during patching.
Unfortunately, due to init ordering, fixmap is still used during
boot-time patching. Future patches can eliminate the need for it.

The second issue is the missing lockdep assertion to ensure text_mutex
is taken. It is actually not always taken, so fix the instances that
were found not to take the lock (although they should be safe even
without taking the lock).

Finally, try to be more conservative and to map a single page, instead
of two, when possible. This helps both security and performance.

In addition, there is some cleanup of the patching code to make it more

- Added handling of error in get_locked_pte()
- Remove lockdep assertion, clarify text_mutex use instead [masami]
- Comment fix [peterz]
- Removed remainders of text_poke return value [masami]
- Use __weak for poking_init instead of macros [masami]
- Simplify error handling in poking_init [masami]

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lkml.org/lkml/2018/8/24/586

Andy Lutomirski (1):
x86/mm: temporary mm struct

Nadav Amit (5):
x86/alternatives: clarify text_mutex use in text_poke
fork: provide a function for copying init_mm
x86/alternatives: initializing temporary mm for patching
x86/alternatives: use temporary mm for text poking
x86/alternatives: remove text_poke() return value

arch/x86/include/asm/mmu_context.h | 20 ++++
arch/x86/include/asm/pgtable.h | 3 +
arch/x86/include/asm/text-patching.h | 4 +-
arch/x86/kernel/alternative.c | 173 +++++++++++++++++++++++----
arch/x86/mm/init_64.c | 29 +++++
include/linux/sched/task.h | 1 +
init/main.c | 3 +
kernel/fork.c | 24 +++-
8 files changed, 226 insertions(+), 31 deletions(-)