From: Sean Christopherson <[email protected]>
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)
Acked-by: Jethro Beekman <[email protected]>
Reviewed-by: Darren Kenny <[email protected]>
Reviewed-by: Borislav Petkov <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>
---
arch/x86/include/asm/trap_pf.h | 1 +
arch/x86/mm/fault.c | 12 ++++++++++++
2 files changed, 13 insertions(+)
diff --git a/arch/x86/include/asm/trap_pf.h b/arch/x86/include/asm/trap_pf.h
index 305bc1214aef..1794777b2a85 100644
--- a/arch/x86/include/asm/trap_pf.h
+++ b/arch/x86/include/asm/trap_pf.h
@@ -19,6 +19,7 @@ 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 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
--
2.27.0