Commit 11e86dc7 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/paravirt: Detect over-sized patching bugs in paravirt_patch_call() 

paravirt_patch_call() currently handles patching failures inconsistently:
we generate a warning in the retpoline case, but don't in other cases where
we might end up with a non-working kernel as well.

So just convert it all to a BUG_ON(), these patching calls are *not* supposed
to fail, and if they do we want to know it immediately.

This also makes the kernel smaller and removes an #ifdef ugly.

I tried it with a richly paravirt-enabled kernel and no patching bugs
were detected.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190425095039.GC115378@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2777cae2

arch/x86/kernel/paravirt.c

+8 −8
Original line number Diff line number Diff line
@@ -73,21 +73,21 @@ struct branch { 
static unsigned paravirt_patch_call(void *insnbuf, const void *target,

				    unsigned long addr, unsigned len)

{

	const int call_len = 5;

	struct branch *b = insnbuf;

	unsigned long delta = (unsigned long)target - (addr+5);

	unsigned long delta = (unsigned long)target - (addr+call_len);



	if (len < 5) {

#ifdef CONFIG_RETPOLINE

		WARN_ONCE(1, "Failing to patch indirect CALL in %ps\n", (void *)addr);

#endif

		return len;	/* call too long for patch site */

	if (len < call_len) {

		pr_warn("paravirt: Failed to patch indirect CALL at %ps\n", (void *)addr);

		/* Kernel might not be viable if patching fails, bail out: */

		BUG_ON(1);

	}



	b->opcode = 0xe8; /* call */

	b->delta = delta;

	BUILD_BUG_ON(sizeof(*b) != 5);

	BUILD_BUG_ON(sizeof(*b) != call_len);



	return 5;

	return call_len;

}



#ifdef CONFIG_PARAVIRT_XXL