[PATCH v4 04/17] x86/insn-eval: Add utility functions to get register offsets

[Ricardo Neri]

The function insn_get_reg_offset takes as argument an enumeration that
indicates the type of offset that is returned: the R/M part of the ModRM
byte, the index of the SIB byte or the base of the SIB byte. Callers of
this function would need the definition of such enumeration. This is not
needed. Instead, helper functions can be defined for this purpose can be
added. 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 mod part of the ModRM byte.

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 |  3 +++
 arch/x86/lib/insn-eval.c         | 51 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 5cab1b1..754211b 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -12,5 +12,8 @@
 #include <asm/ptrace.h>
 
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_sib_base(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 2ebfaa4..6c62fbf 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -98,6 +98,57 @@ 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:	Set of registers indicated by the ModRM byte
+ *
+ * Obtain 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.
+ *
+ * Return: Register indicated by r/m, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs)
+{
+	return get_reg_offset(insn, regs, REG_TYPE_RM);
+}
+
+/**
+ * insn_get_reg_offset_sib_base - Obtain register in base part of SiB byte
+ * @insn:	Instruction structure containing the SiB byte
+ * @regs:	Set of registers indicated by the SiB byte
+ *
+ * Obtain the register indicated by the base part of the SiB 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 SiB does not refer to a register.
+ *
+ * Return: Register indicated by SiB's base, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs)
+{
+	return get_reg_offset(insn, regs, REG_TYPE_BASE);
+}
+
+/**
+ * insn_get_reg_offset_sib_index - Obtain register in index part of SiB byte
+ * @insn:	Instruction structure containing the SiB byte
+ * @regs:	Set of registers indicated by the SiB byte
+ *
+ * Obtain the register indicated by the index part of the SiB byte. The
+ * register is obtained as an offset from the index of pt_regs. In specific
+ * cases, the returned value can be -EDOM to indicate that the particular value
+ * of SiB does not refer to a register.
+ *
+ * Return: Register indicated by SiB's base, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
+{
+	return get_reg_offset(insn, regs, REG_TYPE_INDEX);
+}
+
 /*
  * return the address being referenced be instruction
  * for rm=3 returning the content of the rm reg
-- 
2.9.3