The following commit has been merged into the x86/mm branch of tip: Commit-ID: 56e62cd28aaae2fcbec8af67b05843c47c6da170 Gitweb: https://git.kernel.org/tip/56e62cd28aaae2fcbec8af67b05843c47c6da170 Author: Andy Lutomirski <l...@kernel.org> AuthorDate: Tue, 09 Feb 2021 18:33:38 -08:00 Committer: Borislav Petkov <b...@suse.de> CommitterDate: Wed, 10 Feb 2021 14:13:32 +01:00
x86/fault: Correct a few user vs kernel checks wrt WRUSS In general, page fault errors for WRUSS should be just like get_user(), etc. Fix three bugs in this area: There is a comment that says that, if the kernel can't handle a page fault on a user address due to OOM, the OOM-kill-and-retry logic would be skipped. The code checked kernel *privilege*, not kernel mode, so it missed WRUSS. This means that the kernel would malfunction if it got OOM on a WRUSS fault -- this would be a kernel-mode, user-privilege fault, and the OOM killer would be invoked and the handler would retry the faulting instruction. A failed user access from kernel while a fatal signal is pending should fail even if the instruction in question was WRUSS. do_sigbus() should not send SIGBUS for WRUSS -- it should handle it like any other kernel mode failure. Signed-off-by: Andy Lutomirski <l...@kernel.org> Signed-off-by: Borislav Petkov <b...@suse.de> Link: https://lkml.kernel.org/r/a7b7bcea730bd4069e6b7e629236bb2cf526c2fb.1612924255.git.l...@kernel.org --- arch/x86/mm/fault.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 013910b..b110484 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -945,7 +945,7 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, vm_fault_t fault) { /* Kernel mode? Handle exceptions or die: */ - if (!(error_code & X86_PF_USER)) { + if (!user_mode(regs)) { no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); return; } @@ -1217,7 +1217,14 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, } NOKPROBE_SYMBOL(do_kern_addr_fault); -/* Handle faults in the user portion of the address space */ +/* + * Handle faults in the user portion of the address space. Nothing in here + * should check X86_PF_USER without a specific justification: for almost + * all purposes, we should treat a normal kernel access to user memory + * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction. + * The one exception is AC flag handling, which is, per the x86 + * architecture, special for WRUSS. + */ static inline void do_user_addr_fault(struct pt_regs *regs, unsigned long error_code, @@ -1406,14 +1413,14 @@ good_area: if (likely(!(fault & VM_FAULT_ERROR))) return; - if (fatal_signal_pending(current) && !(error_code & X86_PF_USER)) { + if (fatal_signal_pending(current) && !user_mode(regs)) { no_context(regs, error_code, address, 0, 0); return; } if (fault & VM_FAULT_OOM) { /* Kernel mode? Handle exceptions or die: */ - if (!(error_code & X86_PF_USER)) { + if (!user_mode(regs)) { no_context(regs, error_code, address, SIGSEGV, SEGV_MAPERR); return;
