From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 4 Dec 2017 15:08:00 +0100 Subject: [PATCH] x86/mm: Optimize RESTORE_CR3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 Most NMI/paranoid exceptions will not in fact change pagetables and would thus not require TLB flushing, however RESTORE_CR3 uses flushing CR3 writes. Restores to kernel PCIDs can be NOFLUSH, because we explicitly flush the kernel mappings and now that we track which user PCIDs need flushing we can avoid those too when possible. This does mean RESTORE_CR3 needs an additional scratch_reg, luckily both sites have plenty available. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Will Deacon Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Signed-off-by: Ingo Molnar (cherry picked from commit 21e94459110252d41b45c0c8ba50fd72a664d50c) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit 6ebe6e2896841282357d43c09394b0ca47c41e4a) Signed-off-by: Fabian Grünbichler --- arch/x86/entry/calling.h | 30 ++++++++++++++++++++++++++++-- arch/x86/entry/entry_64.S | 4 ++-- 2 files changed, 30 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index ce5fb309926d..015e0a84bb99 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -280,8 +280,34 @@ For 32-bit we have the following conventions - kernel is built with .Ldone_\@: .endm -.macro RESTORE_CR3 save_reg:req +.macro RESTORE_CR3 scratch_reg:req save_reg:req ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI + + ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID + + /* + * KERNEL pages can always resume with NOFLUSH as we do + * explicit flushes. + */ + bt $X86_CR3_PTI_SWITCH_BIT, \save_reg + jnc .Lnoflush_\@ + + /* + * Check if there's a pending flush for the user ASID we're + * about to set. + */ + movq \save_reg, \scratch_reg + andq $(0x7FF), \scratch_reg + bt \scratch_reg, THIS_CPU_user_pcid_flush_mask + jnc .Lnoflush_\@ + + btr \scratch_reg, THIS_CPU_user_pcid_flush_mask + jmp .Lwrcr3_\@ + +.Lnoflush_\@: + SET_NOFLUSH_BIT \save_reg + +.Lwrcr3_\@: /* * The CR3 write could be avoided when not changing its value, * but would require a CR3 read *and* a scratch register. @@ -300,7 +326,7 @@ For 32-bit we have the following conventions - kernel is built with .endm .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req .endm -.macro RESTORE_CR3 save_reg:req +.macro RESTORE_CR3 scratch_reg:req save_reg:req .endm #endif diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index fb43f14ed299..b48f2c78a9bf 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1300,7 +1300,7 @@ ENTRY(paranoid_exit) testl %ebx, %ebx /* swapgs needed? */ jnz .Lparanoid_exit_no_swapgs TRACE_IRQS_IRETQ - RESTORE_CR3 save_reg=%r14 + RESTORE_CR3 scratch_reg=%rbx save_reg=%r14 SWAPGS_UNSAFE_STACK jmp .Lparanoid_exit_restore .Lparanoid_exit_no_swapgs: @@ -1742,7 +1742,7 @@ end_repeat_nmi: movq $-1, %rsi call do_nmi - RESTORE_CR3 save_reg=%r14 + RESTORE_CR3 scratch_reg=%r15 save_reg=%r14 testl %ebx, %ebx /* swapgs needed? */ jnz nmi_restore -- 2.14.2