[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 
Cc: Adam Buchbinder 
Cc: Colin Ian King 
Cc: Lorenzo Stoakes 
Cc: Qiaowei Ren 
Cc: Arnaldo Carvalho de Melo 
Cc: Masami Hiramatsu 
Cc: Adrian Hunter 
Cc: Kees Cook 
Cc: Thomas Garnier 
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Dmitry Vyukov 
Cc: Ravi V. Shankar 
Cc: [e-mail]
Signed-off-by: Ricardo Neri 
---
 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