[v3 PATCH 04/10] x86/insn-kernel: Add a function to obtain register offset in ModRM

[Ricardo Neri]

The function insn_get_reg_offset requires a type to indicate whether
the returned offset is that given by by the ModRM or the SIB byte.
Callers of this function would need the definition of the type struct.
This is not needed. Instead, auxiliary functions can be defined for
this purpose.

When the operand is a register, the emulation code for User-Mode
Instruction Prevention needs to know the offset of the register indicated
in the r/m part of the ModRM byte. Thus, start by adding an auxiliary
function for this purpose.

Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Adam Buchbinder <adam.buchbinder at gmail.com>
Cc: Colin Ian King <colin.king at canonical.com>
Cc: Lorenzo Stoakes <lstoakes at gmail.com>
Cc: Qiaowei Ren <qiaowei.ren at intel.com>
Cc: Arnaldo Carvalho de Melo <acme at redhat.com>
Cc: Masami Hiramatsu <mhiramat at kernel.org>
Cc: Adrian Hunter <adrian.hunter at intel.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Thomas Garnier <thgarnie at google.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Borislav Petkov <bp at suse.de>
Cc: Dmitry Vyukov <dvyukov at google.com>
Cc: Ravi V. Shankar <ravi.v.shankar at intel.com>
Cc: x86 at kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon at linux.intel.com>
---
 arch/x86/include/asm/insn-kernel.h | 1 +
 arch/x86/lib/insn-kernel.c         | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/insn-kernel.h b/arch/x86/include/asm/insn-kernel.h
index aef416a..3f34649 100644
--- a/arch/x86/include/asm/insn-kernel.h
+++ b/arch/x86/include/asm/insn-kernel.h
@@ -12,5 +12,6 @@
 #include <asm/ptrace.h>
 
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_rm(struct insn *insn, struct pt_regs *regs);
 
 #endif /* _ASM_X86_INSN_KERNEL_H */
diff --git a/arch/x86/lib/insn-kernel.c b/arch/x86/lib/insn-kernel.c
index 8072abe..267cab4 100644
--- a/arch/x86/lib/insn-kernel.c
+++ b/arch/x86/lib/insn-kernel.c
@@ -95,6 +95,11 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 	return regoff[regno];
 }
 
+int insn_get_reg_offset_rm(struct insn *insn, struct pt_regs *regs)
+{
+	return get_reg_offset(insn, regs, REG_TYPE_RM);
+}
+
 /*
  * return the address being referenced be instruction
  * for rm=3 returning the content of the rm reg
-- 
2.9.3