Commit 6cae637f authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Andrew Morton
Browse files

entry: kmsan: introduce kmsan_unpoison_entry_regs() 

struct pt_regs passed into IRQ entry code is set up by uninstrumented asm
functions, therefore KMSAN may not notice the registers are initialized.

kmsan_unpoison_entry_regs() unpoisons the contents of struct pt_regs,
preventing potential false positives.  Unlike kmsan_unpoison_memory(), it
can be called under kmsan_in_runtime(), which is often the case in IRQ
entry code.

Link: https://lkml.kernel.org/r/20220915150417.722975-41-glider@google.com


Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 37ad4ee8

include/linux/kmsan.h

+15 −0
Original line number Diff line number Diff line
@@ -214,6 +214,17 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents, 
 */

void kmsan_handle_urb(const struct urb *urb, bool is_out);



/**

 * kmsan_unpoison_entry_regs() - Handle pt_regs in low-level entry code.

 * @regs:	struct pt_regs pointer received from assembly code.

 *

 * KMSAN unpoisons the contents of the passed pt_regs, preventing potential

 * false positive reports. Unlike kmsan_unpoison_memory(),

 * kmsan_unpoison_entry_regs() can be called from the regions where

 * kmsan_in_runtime() returns true, which is the case in early entry code.

 */

void kmsan_unpoison_entry_regs(const struct pt_regs *regs);



#else



static inline void kmsan_init_shadow(void)
@@ -310,6 +321,10 @@ static inline void kmsan_handle_urb(const struct urb *urb, bool is_out) 
{

}



static inline void kmsan_unpoison_entry_regs(const struct pt_regs *regs)

{

}



#endif



#endif /* _LINUX_KMSAN_H */

kernel/entry/common.c

+5 −0
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <linux/resume_user_mode.h>

#include <linux/highmem.h>

#include <linux/jump_label.h>

#include <linux/kmsan.h>

#include <linux/livepatch.h>

#include <linux/audit.h>

#include <linux/tick.h>
@@ -24,6 +25,7 @@ static __always_inline void __enter_from_user_mode(struct pt_regs *regs) 
	user_exit_irqoff();



	instrumentation_begin();

	kmsan_unpoison_entry_regs(regs);

	trace_hardirqs_off_finish();

	instrumentation_end();

}
@@ -352,6 +354,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs) 
		lockdep_hardirqs_off(CALLER_ADDR0);

		ct_irq_enter();

		instrumentation_begin();

		kmsan_unpoison_entry_regs(regs);

		trace_hardirqs_off_finish();

		instrumentation_end();
@@ -367,6 +370,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs) 
	 */

	lockdep_hardirqs_off(CALLER_ADDR0);

	instrumentation_begin();

	kmsan_unpoison_entry_regs(regs);

	rcu_irq_enter_check_tick();

	trace_hardirqs_off_finish();

	instrumentation_end();
@@ -452,6 +456,7 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs) 
	ct_nmi_enter();



	instrumentation_begin();

	kmsan_unpoison_entry_regs(regs);

	trace_hardirqs_off_finish();

	ftrace_nmi_enter();

	instrumentation_end();

mm/kmsan/hooks.c

+26 −0
Original line number Diff line number Diff line
@@ -348,6 +348,32 @@ void kmsan_unpoison_memory(const void *address, size_t size) 
}

EXPORT_SYMBOL(kmsan_unpoison_memory);



/*

 * Version of kmsan_unpoison_memory() that can be called from within the KMSAN

 * runtime.

 *

 * Non-instrumented IRQ entry functions receive struct pt_regs from assembly

 * code. Those regs need to be unpoisoned, otherwise using them will result in

 * false positives.

 * Using kmsan_unpoison_memory() is not an option in entry code, because the

 * return value of in_task() is inconsistent - as a result, certain calls to

 * kmsan_unpoison_memory() are ignored. kmsan_unpoison_entry_regs() ensures that

 * the registers are unpoisoned even if kmsan_in_runtime() is true in the early

 * entry code.

 */

void kmsan_unpoison_entry_regs(const struct pt_regs *regs)

{

	unsigned long ua_flags;



	if (!kmsan_enabled)

		return;



	ua_flags = user_access_save();

	kmsan_internal_unpoison_memory((void *)regs, sizeof(*regs),

				       KMSAN_POISON_NOCHECK);

	user_access_restore(ua_flags);

}



void kmsan_check_memory(const void *addr, size_t size)

{

	if (!kmsan_enabled)