From: Sean Christopherson Date: Thu, 12 Nov 2020 22:01:17 +0000 (+0200) Subject: x86/mm: Signal SIGSEGV with PF_SGX X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=74faeee06db81a06add0def6a394210c8fef0ab7;p=linux.git 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 --- diff --git a/arch/x86/include/asm/trap_pf.h b/arch/x86/include/asm/trap_pf.h index 305bc1214aef9..10b1de500ab1c 100644 --- a/arch/x86/include/asm/trap_pf.h +++ b/arch/x86/include/asm/trap_pf.h @@ -11,6 +11,7 @@ * bit 3 == 1: use of reserved bit detected * bit 4 == 1: fault was an instruction fetch * bit 5 == 1: protection keys block access + * bit 15 == 1: SGX MMU page-fault */ enum x86_pf_error_code { X86_PF_PROT = 1 << 0, @@ -19,6 +20,7 @@ enum x86_pf_error_code { X86_PF_RSVD = 1 << 3, X86_PF_INSTR = 1 << 4, X86_PF_PK = 1 << 5, + X86_PF_SGX = 1 << 15, }; #endif /* _ASM_X86_TRAP_PF_H */ diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 82bf37a5c9ecc..9339fee837845 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