[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Thu, 05 May 2022 23:56:12 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Alexander Potapenko <glider@...gle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrey Konovalov <andreyknvl@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Christoph Hellwig <hch@....de>,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Ilya Leoshkevich <iii@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Kees Cook <keescook@...omium.org>,
Marco Elver <elver@...gle.com>,
Mark Rutland <mark.rutland@....com>,
Matthew Wilcox <willy@...radead.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
Pekka Enberg <penberg@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vegard Nossum <vegard.nossum@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>,
kasan-dev <kasan-dev@...glegroups.com>,
Linux Memory Management List <linux-mm@...ck.org>,
Linux-Arch <linux-arch@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 28/46] kmsan: entry: handle register passing from
uninstrumented code
Alexander,
On Thu, May 05 2022 at 20:04, Alexander Potapenko wrote:
> On Tue, May 3, 2022 at 12:00 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>> > Regarding the regs, you are right. It should be enough to unpoison the
>> > regs at idtentry prologue instead.
>> > I tried that initially, but IIRC it required patching each of the
>> > DEFINE_IDTENTRY_XXX macros, which already use instrumentation_begin().
>>
>> Exactly 4 instances :)
>>
>
> Not really, I had to add a call to `kmsan_unpoison_memory(regs,
> sizeof(*regs));` to the following places in
> arch/x86/include/asm/idtentry.h:
> - DEFINE_IDTENTRY()
> - DEFINE_IDTENTRY_ERRORCODE()
> - DEFINE_IDTENTRY_RAW()
> - DEFINE_IDTENTRY_RAW_ERRORCODE()
> - DEFINE_IDTENTRY_IRQ()
> - DEFINE_IDTENTRY_SYSVEC()
> - DEFINE_IDTENTRY_SYSVEC_SIMPLE()
> - DEFINE_IDTENTRY_DF()
>
> , but even that wasn't enough. For some reason I also had to unpoison
> pt_regs directly in
> DEFINE_IDTENTRY_SYSVEC(sysvec_apic_timer_interrupt) and
> DEFINE_IDTENTRY_IRQ(common_interrupt).
> In the latter case, this could have been caused by
> asm_common_interrupt being entered from irq_entries_start(), but I am
> not sure what is so special about sysvec_apic_timer_interrupt().
>
> Ideally, it would be great to find that single point where pt_regs are
> set up before being passed to all IDT entries.
> I used to do that by inserting calls to kmsan_unpoison_memory right
> into arch/x86/entry/entry_64.S
> (https://github.com/google/kmsan/commit/3b0583f45f74f3a09f4c7e0e0588169cef918026),
> but that required storing/restoring all GP registers. Maybe there's a
> better way?
Yes. Something like this should cover all exceptions and syscalls before
anything instrumentable can touch @regs. Anything up to those points is
either off-limit for instrumentation or does not deal with @regs.
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -24,6 +24,7 @@ static __always_inline void __enter_from
user_exit_irqoff();
instrumentation_begin();
+ unpoison(regs);
trace_hardirqs_off_finish();
instrumentation_end();
}
@@ -352,6 +353,7 @@ noinstr irqentry_state_t irqentry_enter(
lockdep_hardirqs_off(CALLER_ADDR0);
rcu_irq_enter();
instrumentation_begin();
+ unpoison(regs);
trace_hardirqs_off_finish();
instrumentation_end();
@@ -367,6 +369,7 @@ noinstr irqentry_state_t irqentry_enter(
*/
lockdep_hardirqs_off(CALLER_ADDR0);
instrumentation_begin();
+ unpoison(regs);
rcu_irq_enter_check_tick();
trace_hardirqs_off_finish();
instrumentation_end();
@@ -452,6 +455,7 @@ irqentry_state_t noinstr irqentry_nmi_en
rcu_nmi_enter();
instrumentation_begin();
+ unpoison(regs);
trace_hardirqs_off_finish();
ftrace_nmi_enter();
instrumentation_end();
As I said: 4 places :)
> Fortunately, I don't think we need to insert extra instrumentation
> into instrumentation_begin()/instrumentation_end() regions.
>
> What I have in mind is adding a bool flag to kmsan_context_state, that
> the instrumentation sets to true before the function call.
> When entering an instrumented function, KMSAN would check that flag
> and set it to false, so that the context state can be only used once.
> If a function is called from another instrumented function, the
> context state is properly set up, and there is nothing to worry about.
> If it is called from non-instrumented code (either noinstr or the
> skipped files that have KMSAN_SANITIZE:=n), KMSAN would detect that
> and wipe the context state before use.
Sounds good.
Thanks,
tglx
Powered by blists - more mailing lists