x86/umip: Factor out instruction decoding
Factor out the code used to decode an instruction with the correct
address and operand sizes to a helper function.
No functional changes.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-10-joro@8bytes.org
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 947b7f1..2323c85 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1405,3 +1405,48 @@ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
return MAX_INSN_SIZE - not_copied;
}
+
+/**
+ * insn_decode() - Decode an instruction
+ * @insn: Structure to store decoded instruction
+ * @regs: Structure with register values as seen when entering kernel mode
+ * @buf: Buffer containing the instruction bytes
+ * @buf_size: Number of instruction bytes available in buf
+ *
+ * Decodes the instruction provided in buf and stores the decoding results in
+ * insn. Also determines the correct address and operand sizes.
+ *
+ * Returns:
+ *
+ * True if instruction was decoded, False otherwise.
+ */
+bool insn_decode(struct insn *insn, struct pt_regs *regs,
+ unsigned char buf[MAX_INSN_SIZE], int buf_size)
+{
+ int seg_defs;
+
+ insn_init(insn, buf, buf_size, user_64bit_mode(regs));
+
+ /*
+ * Override the default operand and address sizes with what is specified
+ * in the code segment descriptor. The instruction decoder only sets
+ * the address size it to either 4 or 8 address bytes and does nothing
+ * for the operand bytes. This OK for most of the cases, but we could
+ * have special cases where, for instance, a 16-bit code segment
+ * descriptor is used.
+ * If there is an address override prefix, the instruction decoder
+ * correctly updates these values, even for 16-bit defaults.
+ */
+ seg_defs = insn_get_code_seg_params(regs);
+ if (seg_defs == -EINVAL)
+ return false;
+
+ insn->addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
+ insn->opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
+
+ insn_get_length(insn);
+ if (buf_size < insn->length)
+ return false;
+
+ return true;
+}