x86/sgx: Remove .fixup usage

Create EX_TYPE_FAULT_SGX which does as EX_TYPE_FAULT does, except adds
this extra bit that SGX really fancies having.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211110101325.961246679@infradead.org

Author: Peter Zijlstra

arch/x86/include/asm/extable_fixup_types.h

@@ -48,4 +48,6 @@
 #define	EX_TYPE_ZERO_REG		(EX_TYPE_IMM_REG | EX_DATA_IMM(0))
 #define	EX_TYPE_ONE_REG			(EX_TYPE_IMM_REG | EX_DATA_IMM(1))
 
+#define	EX_TYPE_FAULT_SGX		18
+
 #endif

arch/x86/include/asm/sgx.h

@@ -45,6 +45,24 @@ enum sgx_encls_function {
 	EMODT	= 0x0F,
 };
 
+/**
+ * SGX_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 SGX_ENCLS_FAULT_FLAG 0x40000000
+
 /**
  * enum sgx_return_code - The return code type for ENCLS, ENCLU and ENCLV
  * %SGX_NOT_TRACKED:		Previous ETRACK's shootdown sequence has not

arch/x86/kernel/cpu/sgx/encls.h

@@ -11,26 +11,8 @@
 #include <asm/traps.h>
 #include "sgx.h"
 
-/**
- * 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
-
 /* Retrieve the encoded trapnr from the specified return code. */
-#define ENCLS_TRAPNR(r) ((r) & ~ENCLS_FAULT_FLAG)
+#define ENCLS_TRAPNR(r) ((r) & ~SGX_ENCLS_FAULT_FLAG)
 
 /* Issue a WARN() about an ENCLS function. */
 #define ENCLS_WARN(r, name) {						  \
@@ -50,7 +32,7 @@
  */
 static inline bool encls_faulted(int ret)
 {
-	return ret & ENCLS_FAULT_FLAG;
+	return ret & SGX_ENCLS_FAULT_FLAG;
 }
 
 /**
@@ -88,11 +70,7 @@ static inline bool encls_failed(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)				\
+	_ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_FAULT_SGX)		\
 	: "=a"(ret)						\
 	: "a"(rax), inputs					\
 	: "memory", "cc");					\
@@ -127,7 +105,7 @@ static inline bool encls_failed(int ret)
  *
  * Return:
  *   0 on success,
- *   trapnr with ENCLS_FAULT_FLAG set on fault
+ *   trapnr with SGX_ENCLS_FAULT_FLAG set on fault
  */
 #define __encls_N(rax, rbx_out, inputs...)			\
 	({							\
@@ -136,11 +114,7 @@ static inline bool encls_failed(int ret)
 	"1: .byte 0x0f, 0x01, 0xcf;\n\t"			\
 	"   xor %%eax,%%eax;\n"					\
 	"2:\n"							\
-	".section .fixup,\"ax\"\n"				\
-	"3: orl $"__stringify(ENCLS_FAULT_FLAG)",%%eax\n"	\
-	"   jmp 2b\n"						\
-	".previous\n"						\
-	_ASM_EXTABLE_FAULT(1b, 3b)				\
+	_ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_FAULT_SGX)		\
 	: "=a"(ret), "=b"(rbx_out)				\
 	: "a"(rax), inputs					\
 	: "memory");						\

arch/x86/mm/extable.c

@@ -10,6 +10,7 @@
 #include <asm/traps.h>
 #include <asm/kdebug.h>
 #include <asm/insn-eval.h>
+#include <asm/sgx.h>
 
 static inline unsigned long *pt_regs_nr(struct pt_regs *regs, int nr)
 {
@@ -47,6 +48,13 @@ static bool ex_handler_fault(const struct exception_table_entry *fixup,
 	return ex_handler_default(fixup, regs);
 }
 
+static bool ex_handler_sgx(const struct exception_table_entry *fixup,
+			   struct pt_regs *regs, int trapnr)
+{
+	regs->ax = trapnr | SGX_ENCLS_FAULT_FLAG;
+	return ex_handler_default(fixup, regs);
+}
+
 /*
  * Handler for when we fail to restore a task's FPU state.  We should never get
  * here because the FPU state of a task using the FPU (task->thread.fpu.state)
@@ -207,6 +215,8 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
 		return ex_handler_pop_zero(e, regs);
 	case EX_TYPE_IMM_REG:
 		return ex_handler_imm_reg(e, regs, reg, imm);
+	case EX_TYPE_FAULT_SGX:
+		return ex_handler_sgx(e, regs, trapnr);
 	}
 	BUG();
 }