Commit-ID: e50928d7213e72ee95507221a89ed07d2bb6517b Gitweb: https://git.kernel.org/tip/e50928d7213e72ee95507221a89ed07d2bb6517b Author: Andy Lutomirski <[email protected]> AuthorDate: Mon, 19 Nov 2018 14:45:29 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 20 Nov 2018 08:44:29 +0100
x86/fault: Fix SMAP #PF handling buglet for implicit supervisor accesses Currently, if a user program somehow triggers an implicit supervisor access to a user address (e.g. if the kernel somehow sets LDTR to a user address), it will be incorrectly detected as a SMAP violation if AC is clear and SMAP is enabled. This is incorrect -- the error has nothing to do with SMAP. Fix the condition so that only accesses with the hardware USER bit set are diagnosed as SMAP violations. With the logic fixed, an implicit supervisor access to a user address will hit the code lower in the function that is intended to handle it even if SMAP is enabled. That logic is still a bit buggy, and later patches will clean it up. I *think* this code is still correct for WRUSS, and I've added a comment to that effect. Signed-off-by: Andy Lutomirski <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Yu-cheng Yu <[email protected]> Link: http://lkml.kernel.org/r/d1d1b2e66ef31f884dba172084486ea9423ddcdb.1542667307.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/mm/fault.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 9d092ab74f18..7a69b66cf071 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1235,12 +1235,15 @@ void do_user_addr_fault(struct pt_regs *regs, pgtable_bad(regs, hw_error_code, address); /* - * If SMAP is on, check for invalid kernel (supervisor) - * access to user pages in the user address space. + * If SMAP is on, check for invalid kernel (supervisor) access to user + * pages in the user address space. The odd case here is WRUSS, + * which, according to the preliminary documentation, does not respect + * SMAP and will have the USER bit set so, in all cases, SMAP + * enforcement appears to be consistent with the USER bit. */ if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) && !(hw_error_code & X86_PF_USER) && - (user_mode(regs) || !(regs->flags & X86_EFLAGS_AC)))) + !(regs->flags & X86_EFLAGS_AC))) { bad_area_nosemaphore(regs, hw_error_code, address); return;
