From 74faeee06db81a06add0def6a394210c8fef0ab7 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 13 Nov 2020 00:01:17 +0200 Subject: x86/mm: Signal SIGSEGV with PF_SGX The x86 architecture has a set of page fault error codes. These indicate things like whether the fault occurred from a write, or whether it originated in userspace. The SGX hardware architecture has its own per-page memory management metadata (EPCM) [*] and hardware which is separate from the normal x86 MMU. The architecture has a new page fault error code: PF_SGX. This new error code bit is set whenever a page fault occurs as the result of the SGX MMU. These faults occur for a variety of reasons. For instance, an access attempt to enclave memory from outside the enclave causes a PF_SGX fault. PF_SGX would also be set for permission conflicts, such as if a write to an enclave page occurs and the page is marked read-write in the x86 page tables but is read-only in the EPCM. These faults do not always indicate errors, though. SGX pages are encrypted with a key that is destroyed at hardware reset, including suspend. Throwing a SIGSEGV allows user space software to react and recover when these events occur. Include PF_SGX in the PF error codes list and throw SIGSEGV when it is encountered. [*] Intel SDM: 36.5.1 Enclave Page Cache Map (EPCM) [ bp: Add bit 15 to the comment above enum x86_pf_error_code too. ] Signed-off-by: Sean Christopherson Signed-off-by: Jarkko Sakkinen Signed-off-by: Borislav Petkov Acked-by: Jethro Beekman Link: https://lkml.kernel.org/r/20201112220135.165028-7-jarkko@kernel.org --- arch/x86/mm/fault.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch/x86/mm') diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 82bf37a5c9ec..9339fee83784 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1101,6 +1101,18 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) if (error_code & X86_PF_PK) return 1; + /* + * SGX hardware blocked the access. This usually happens + * when the enclave memory contents have been destroyed, like + * after a suspend/resume cycle. In any case, the kernel can't + * fix the cause of the fault. Handle the fault as an access + * error even in cases where no actual access violation + * occurred. This allows userspace to rebuild the enclave in + * response to the signal. + */ + if (unlikely(error_code & X86_PF_SGX)) + return 1; + /* * Make sure to check the VMA so that we do not perform * faults just to hit a X86_PF_PK as soon as we fill in a -- cgit v1.2.3