From b2e59f5827851abff8dc4ba09c9d13470a389f1f Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 8 Oct 2017 21:53:05 -0700 Subject: [PATCH] x86/mm/64: Fix reboot interaction with CR4.PCIDE commit 924c6b900cfdf376b07bccfd80e62b21914f8a5a upstream. Trying to reboot via real mode fails with PCID on: long mode cannot be exited while CR4.PCIDE is set. (No, I have no idea why, but the SDM and actual CPUs are in agreement here.) The result is a GPF and a hang instead of a reboot. I didn't catch this in testing because neither my computer nor my VM reboots this way. I can trigger it with reboot=bios, though. Fixes: 660da7c9228f ("x86/mm: Enable CR4.PCIDE on supported systems") Reported-and-tested-by: Steven Rostedt (VMware) Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Cc: Borislav Petkov Link: https://lkml.kernel.org/r/f1e7d965998018450a7a70c2823873686a8b21c0.1507524746.git.luto@kernel.org Cc: Hugh Dickins Signed-off-by: Greg Kroah-Hartman (cherry picked from commit 6c4db09c291a19da66512f99c4bcb378a862f9e6) Orabug: 27333760 CVE: CVE-2017-5754 Signed-off-by: Pavel Tatashin Signed-off-by: Kirtikar Kashyap --- arch/x86/kernel/reboot.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index ca051c8fb8ba..8af8cd8bdea3 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -93,6 +93,10 @@ void __noreturn machine_real_restart(unsigned int type) load_cr3(initial_page_table); #else write_cr3(real_mode_header->trampoline_pgd); + + /* Exiting long mode will fail if CR4.PCIDE is set. */ + if (static_cpu_has(X86_FEATURE_PCID)) + cr4_clear_bits(X86_CR4_PCIDE); #endif /* Jump to the identity-mapped low memory code */ -- 2.50.1