Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" | Date | Sun, 2 Sep 2018 10:32:19 -0700 |
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text_mutex is expected to be held before text_poke() is called, but we cannot add a lockdep assertion since kgdb does not take it, and instead *supposedly* ensures the lock is not taken and will not be acquired by any other core while text_poke() is running.
The reason for the "supposedly" comment is that it is not entirely clear that this would be the case if gdb_do_roundup is zero.
Add a comment to clarify this behavior, and restore the assertions as they were before the recent commit.
This partially reverts commit 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
Cc: Jiri Kosina <jkosina@suse.cz> Cc: Andy Lutomirski <luto@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Dave Hansen <dave.hansen@intel.com> Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()") Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Tested-by: Masami Hiramatsu <mhiramat@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Nadav Amit <namit@vmware.com> --- arch/x86/kernel/alternative.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index b9d5e7c9ef43..e9be18245698 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -684,6 +684,11 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode, * It means the size must be writable atomically and the address must be aligned * in a way that permits an atomic write. It also makes sure we fit on a single * page. + * + * Context: Must be called under text_mutex. kgdb is an exception: it does not + * hold the mutex, as it *supposedly* ensures that no other core is + * holding the mutex and ensures that none of them will acquire the + * mutex while the code runs. */ void *text_poke(void *addr, const void *opcode, size_t len) { @@ -698,8 +703,6 @@ void *text_poke(void *addr, const void *opcode, size_t len) */ BUG_ON(!after_bootmem); - lockdep_assert_held(&text_mutex); - if (!core_kernel_text((unsigned long)addr)) { pages[0] = vmalloc_to_page(addr); pages[1] = vmalloc_to_page(addr + PAGE_SIZE); -- 2.17.1
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