From 11e86dc7f2746210f9c7dc10deaa7658f8dc8350 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 25 Apr 2019 11:50:39 +0200 Subject: [PATCH] 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 Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20190425095039.GC115378@gmail.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/paravirt.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 7f9121f2fdac..544d386ded45 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -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 -- 2.45.2