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SubjectRe: [PATCH v22 07/24] x86/sgx: Add wrappers for ENCLS leaf functions
On Fri, Oct 04, 2019 at 11:45:13AM +0200, Borislav Petkov wrote:
> On Tue, Sep 03, 2019 at 05:26:38PM +0300, Jarkko Sakkinen wrote:
> > +/**
> > + * ENCLS_FAULT_FLAG - flag signifying an ENCLS return code is a trapnr
> > + *
> > + * ENCLS has its own (positive value) error codes and also generates
> > + * ENCLS specific #GP and #PF faults. And the ENCLS values get munged
> > + * with system error codes as everything percolates back up the stack.
> > + * Unfortunately (for us), we need to precisely identify each unique
> > + * error code, e.g. the action taken if EWB fails varies based on the
> > + * type of fault and on the exact SGX error code, i.e. we can't simply
> > + * convert all faults to -EFAULT.
> > + *
> > + * To make all three error types coexist, we set bit 30 to identify an
> > + * ENCLS fault. Bit 31 (technically bits N:31) is used to differentiate
> > + * between positive (faults and SGX error codes) and negative (system
> > + * error codes) values.
> > + */
> > +#define ENCLS_FAULT_FLAG 0x40000000
>
> BIT(30)

This is intentionally open coded so that it can be stringified in asm.
Alternatively, the asm could use the raw value or a different define. Is
there a third option?

#define __encls_ret_N(rax, inputs...) \
({ \
int ret; \
asm volatile( \
"1: .byte 0x0f, 0x01, 0xcf;\n\t" \
"2:\n" \
".section .fixup,\"ax\"\n" \
"3: orl $"__stringify(ENCLS_FAULT_FLAG)",%%eax\n" \ <----
" jmp 2b\n" \
".previous\n" \
_ASM_EXTABLE_FAULT(1b, 3b) \
: "=a"(ret) \
: "a"(rax), inputs \
: "memory", "cc"); \
ret; \
})

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