[PATCH v7 08/26] x86/insn-eval: Add a utility function to get register offsets

[Ricardo Neri]

The function get_reg_offset() returns the offset to the register the
argument specifies as indicated in an enumeration of type offset. Callers
of this function would need the definition of such enumeration. This is
not needed. Instead, add helper functions for this purpose. These functions
are useful in cases when, for instance, the caller needs to decide whether
the operand is a register or a memory location by looking at the rm part
of the ModRM byte. As of now, this is the only helper function that is
needed.

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-eval.h |  1 +
 arch/x86/lib/insn-eval.c         | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 5cab1b1..7e8c963 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.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_modrm_rm_off(struct insn *insn, struct pt_regs *regs);

#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 182e2ae..8b16761 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -97,6 +97,21 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
    return regoff[regno];
 }

+/**
+ * insn_get_reg_offset_modrm_rm() - Obtain register in r/m part of ModRM byte
+ * @insn:	Instruction structure containing the ModRM byte
+ * @regs:	Structure with register values as seen when entering kernel mode
+ *
+ * Return: The register indicated by the r/m part of the ModRM byte. The
+ * register is obtained as an offset from the base of pt_regs. In specific
+ * cases, the returned value can be -EDOM to indicate that the particular value
+ * of ModRM does not refer to a register and shall be ignored.
+ */
+int insn_get_modrm_rm_off(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