[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 <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-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
-- 
2.9.3