From 367e3f1d3fc9bbf1e626da7aea527f40babf8079 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Fri, 28 Sep 2018 09:02:31 -0700 Subject: x86/mm: Remove spurious fault pkey check Spurious faults only ever occur in the kernel's address space. They are also constrained specifically to faults with one of these error codes: X86_PF_WRITE | X86_PF_PROT X86_PF_INSTR | X86_PF_PROT So, it's never even possible to reach spurious_kernel_fault_check() with X86_PF_PK set. In addition, the kernel's address space never has pages with user-mode protections. Protection Keys are only enforced on pages with user-mode protection. This gives us lots of reasons to not check for protection keys in our sprurious kernel fault handling. But, let's also add some warnings to ensure that these assumptions about protection keys hold true. Cc: x86@kernel.org Cc: Jann Horn Cc: Sean Christopherson Cc: Thomas Gleixner Cc: Andy Lutomirski Signed-off-by: Dave Hansen Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/20180928160231.243A0D6A@viggo.jf.intel.com --- arch/x86/mm/fault.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'arch/x86/mm') diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 7e0fa7e24168..a16652982f98 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1037,12 +1037,6 @@ static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte) if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) return 0; - /* - * Note: We do not do lazy flushing on protection key - * changes, so no spurious fault will ever set X86_PF_PK. - */ - if ((error_code & X86_PF_PK)) - return 1; return 1; } @@ -1217,6 +1211,13 @@ static void do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, unsigned long address) { + /* + * Protection keys exceptions only happen on user pages. We + * have no user pages in the kernel portion of the address + * space, so do not expect them here. + */ + WARN_ON_ONCE(hw_error_code & X86_PF_PK); + /* * We can fault-in kernel-space virtual memory on-demand. The * 'reference' page table is init_mm.pgd. -- cgit v1.2.3