On Wed, Jan 16, 2019 at 04:32:43PM -0800, Rick Edgecombe wrote:
> From: Nadav Amit <namit@xxxxxxxxxx>
>
> text_mutex is currently expected to be held before text_poke() is
> called, but we kgdb does not take the mutex, 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.
I guess that variable name is "kgdb_do_roundup" ?
> This patch creates two wrapper functions, text_poke() and
Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.
Also, do
$ git grep 'This patch' Documentation/process
for more details.
> text_poke_kgdb() which do or do not run the lockdep assertion
> respectively.
>
> While we are at it, change the return code of text_poke() to something
> meaningful. One day, callers might actually respect it and the existing
> BUG_ON() when patching fails could be removed. For kgdb, the return
> value can actually be used.
>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Acked-by: Jiri Kosina <jkosina@xxxxxxx>
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
> arch/x86/include/asm/text-patching.h | 1 +
> arch/x86/kernel/alternative.c | 52 ++++++++++++++++++++--------
> arch/x86/kernel/kgdb.c | 11 +++---
> 3 files changed, 45 insertions(+), 19 deletions(-)
...
> +/**
> + * text_poke_kgdb - Update instructions on a live kernel by kgdb
> + * @addr: address to modify
> + * @opcode: source of the copy
> + * @len: length to copy
> + *
> + * Only atomic text poke/set should be allowed when not doing early patching.
> + * 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: should only be used by kgdb, which ensures no other core is running,
> + * despite the fact it does not hold the text_mutex.
> + */
> +void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
text_poke_unlocked() I guess. I don't think kgdb is that special that it
needs its own function flavor.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
