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Message-ID: <20190125093052.GA27998@zn.tnic>
Date: Fri, 25 Jan 2019 10:30:52 +0100
From: Borislav Petkov <bp@...en8.de>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
Thomas Gleixner <tglx@...utronix.de>,
Nadav Amit <nadav.amit@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>, linux_dti@...oud.com,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org, akpm@...ux-foundation.org,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
will.deacon@....com, ard.biesheuvel@...aro.org,
kristen@...ux.intel.com, deneen.t.dock@...el.com,
Nadav Amit <namit@...are.com>, Kees Cook <keescook@...omium.org>,
Dave Hansen <dave.hansen@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 01/17] Fix "x86/alternatives: Lockdep-enforce text_mutex
in text_poke*()"
On Wed, Jan 16, 2019 at 04:32:43PM -0800, Rick Edgecombe wrote:
> From: Nadav Amit <namit@...are.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@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Acked-by: Jiri Kosina <jkosina@...e.cz>
> Signed-off-by: Nadav Amit <namit@...are.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.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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