Messages in this thread | | | Date | Fri, 25 Jan 2019 10:30:52 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 01/17] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" |
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On Wed, Jan 16, 2019 at 04:32:43PM -0800, Rick Edgecombe wrote: > From: Nadav Amit <namit@vmware.com> > > 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@kernel.org> > Cc: Kees Cook <keescook@chromium.org> > Cc: Dave Hansen <dave.hansen@intel.com> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()") > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Acked-by: Jiri Kosina <jkosina@suse.cz> > Signed-off-by: Nadav Amit <namit@vmware.com> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > --- > 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.
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