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 patch-set). 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 readable. RFC->v1: - 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(-) -- 2.17.1
