Ok, I tried to be as specific as possible in the commit message so that we don't forget. Please lemme know if I've missed something.
Babu, Jim, I'd appreciate it if you ran this to confirm. Thx. --- From: Borislav Petkov <b...@suse.de> Date: Thu, 25 Mar 2021 11:02:31 +0100 Jim Mattson reported that Debian 9 guests using a 4.9-stable kernel are exploding during alternatives patching: kernel BUG at /build/linux-dqnRSc/linux-4.9.228/arch/x86/kernel/alternative.c:709! invalid opcode: 0000 [#1] SMP Modules linked in: CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.9.0-13-amd64 #1 Debian 4.9.228-1 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: swap_entry_free swap_entry_free text_poke_bp swap_entry_free arch_jump_label_transform set_debug_rodata __jump_label_update static_key_slow_inc frontswap_register_ops init_zswap init_frontswap do_one_initcall set_debug_rodata kernel_init_freeable rest_init kernel_init ret_from_fork triggering the BUG_ON in text_poke() which verifies whether patched instruction bytes have actually landed at the destination. Further debugging showed that the TLB flush before that check is insufficient because there could be global mappings left in the TLB, leading to a stale mapping getting used. I say "global mappings" because the hardware configuration is a new one: machine is an AMD, which means, KAISER/PTI doesn't need to be enabled there, which also means there's no user/kernel pagetables split and therefore the TLB can have global mappings. And the configuration is new one for a second reason: because that AMD machine supports PCID and INVPCID, which leads the CPU detection code to set the synthetic X86_FEATURE_INVPCID_SINGLE flag. Now, __native_flush_tlb_single() does invalidate global mappings when X86_FEATURE_INVPCID_SINGLE is *not* set and returns. When X86_FEATURE_INVPCID_SINGLE is set, however, it invalidates the requested address from both PCIDs in the KAISER-enabled case. But if KAISER is not enabled and the machine has global mappings in the TLB, then those global mappings do not get invalidated, which would lead to the above mismatch from using a stale TLB entry. So make sure to flush those global mappings in the KAISER disabled case. Co-debugged by Babu Moger <babu.mo...@amd.com>. Reported-by: Jim Mattson <jmatt...@google.com> Signed-off-by: Borislav Petkov <b...@suse.de> Link: https://lkml.kernel.org/r/CALMp9eRDSW66%2BXvbHVF4ohL7XhThoPoT0BrB0TcS0cgk=dk...@mail.gmail.com --- arch/x86/include/asm/tlbflush.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index f5ca15622dc9..2bfa4deb8cae 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -245,12 +245,15 @@ static inline void __native_flush_tlb_single(unsigned long addr) * ASID. But, userspace flushes are probably much more * important performance-wise. * - * Make sure to do only a single invpcid when KAISER is - * disabled and we have only a single ASID. + * In the KAISER disabled case, do an INVLPG to make sure + * the mapping is flushed in case it is a global one. */ - if (kaiser_enabled) + if (kaiser_enabled) { invpcid_flush_one(X86_CR3_PCID_ASID_USER, addr); - invpcid_flush_one(X86_CR3_PCID_ASID_KERN, addr); + invpcid_flush_one(X86_CR3_PCID_ASID_KERN, addr); + } else { + asm volatile("invlpg (%0)" ::"r" (addr) : "memory"); + } } static inline void __flush_tlb_all(void) -- 2.29.2 -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
