From c1f831425fe900fd18789733b66f4c987345296c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 16 Aug 2023 12:44:19 +0200 Subject: [PATCH] x86/static_call: Fix __static_call_fixup() commit 54097309620ef0dc2d7083783dc521c6a5fef957 upstream. Christian reported spurious module load crashes after some of Song's module memory layout patches. Turns out that if the very last instruction on the very last page of the module is a 'JMP __x86_return_thunk' then __static_call_fixup() will trip a fault and die. And while the module rework made this slightly more likely to happen, it's always been possible. Fixes: ee88d363d156 ("x86,static_call: Use alternative RET encoding") Reported-by: Christian Bricart Signed-off-by: Peter Zijlstra (Intel) Acked-by: Josh Poimboeuf Link: https://lkml.kernel.org/r/20230816104419.GA982867@hirez.programming.kicks-ass.net Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/static_call.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index a9b54b7..3fbb491 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -184,6 +184,19 @@ EXPORT_SYMBOL_GPL(arch_static_call_transform); */ bool __static_call_fixup(void *tramp, u8 op, void *dest) { + unsigned long addr = (unsigned long)tramp; + /* + * Not all .return_sites are a static_call trampoline (most are not). + * Check if the 3 bytes after the return are still kernel text, if not, + * then this definitely is not a trampoline and we need not worry + * further. + * + * This avoids the memcmp() below tripping over pagefaults etc.. + */ + if (((addr >> PAGE_SHIFT) != ((addr + 7) >> PAGE_SHIFT)) && + !kernel_text_address(addr + 7)) + return false; + if (memcmp(tramp+5, tramp_ud, 3)) { /* Not a trampoline site, not our problem. */ return false; -- 2.7.4