Commit 74faeee0 authored by Sean Christopherson's avatar Sean Christopherson Committed by Borislav Petkov
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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: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarJethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-7-jarkko@kernel.org
parent e7e05452

arch/x86/include/asm/trap_pf.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/mm/fault.c

+12 −0
Original line number Diff line number Diff line
@@ -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