From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 30 Dec 2017 22:13:54 +0100 Subject: [PATCH] x86/mm: Remove preempt_disable/enable() from __native_flush_tlb() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 The preempt_disable/enable() pair in __native_flush_tlb() was added in commit: 5cf0791da5c1 ("x86/mm: Disable preemption during CR3 read+write") ... to protect the UP variant of flush_tlb_mm_range(). That preempt_disable/enable() pair should have been added to the UP variant of flush_tlb_mm_range() instead. The UP variant was removed with commit: ce4a4e565f52 ("x86/mm: Remove the UP asm/tlbflush.h code, always use the (formerly) SMP code") ... but the preempt_disable/enable() pair stayed around. The latest change to __native_flush_tlb() in commit: 6fd166aae78c ("x86/mm: Use/Fix PCID to optimize user/kernel switches") ... added an access to a per CPU variable outside the preempt disabled regions, which makes no sense at all. __native_flush_tlb() must always be called with at least preemption disabled. Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch bad callers independent of the smp_processor_id() debugging. Signed-off-by: Thomas Gleixner Cc: Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Dominik Brodowski Cc: Linus Torvalds Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20171230211829.679325424@linutronix.de Signed-off-by: Ingo Molnar (cherry picked from commit decab0888e6e14e11d53cefa85f8b3d3b45ce73c) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit cfcf931c425b60d0092bcb4a4deb1f5d5db0e293) Signed-off-by: Fabian Grünbichler --- arch/x86/include/asm/tlbflush.h | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 7a04a1f1ca11..ff6a6d668c32 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -334,15 +334,17 @@ static inline void invalidate_user_asid(u16 asid) */ static inline void __native_flush_tlb(void) { - invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); /* - * If current->mm == NULL then we borrow a mm which may change - * during a task switch and therefore we must not be preempted - * while we write CR3 back: + * Preemption or interrupts must be disabled to protect the access + * to the per CPU variable and to prevent being preempted between + * read_cr3() and write_cr3(). */ - preempt_disable(); + WARN_ON_ONCE(preemptible()); + + invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); + + /* If current->mm == NULL then the read_cr3() "borrows" an mm */ native_write_cr3(__native_read_cr3()); - preempt_enable(); } /* -- 2.14.2