x86/extable: Extend extable functionality

In order to remove further .fixup usage, extend the extable
infrastructure to take additional information from the extable entry
sites.

Specifically add _ASM_EXTABLE_TYPE_REG() and EX_TYPE_IMM_REG that
extend the existing _ASM_EXTABLE_TYPE() by taking an additional
register argument and encoding that and an s16 immediate into the
existing s32 type field. This limits the actual types to the first
byte, 255 seem plenty.

Also add a few flags into the type word, specifically CLEAR_AX and
CLEAR_DX which clear the return and extended return register.

Notes:
 - due to the % in our register names it's hard to make it more
   generally usable as arm64 did.
 - the s16 is far larger than used in these patches, future extentions
   can easily shrink this to get more bits.
 - without the bitfield fix this will not compile, because: 0xFF > -1
   and we can't even extract the TYPE field.

[nathanchance: Build fix for clang-lto builds:
 https://lkml.kernel.org/r/20211210234953.3420108-1-nathan@kernel.org
]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20211110101325.303890153@infradead.org

1 files changed, 42 insertions, 24 deletions

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index eb3ccffb9b9d..7760d228041b 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -412,32 +412,39 @@ static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx)
 #endif /* CONFIG_X86_64 */
 }
 
-static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
-			  enum reg_type type)
+static const int pt_regoff[] = {
+	offsetof(struct pt_regs, ax),
+	offsetof(struct pt_regs, cx),
+	offsetof(struct pt_regs, dx),
+	offsetof(struct pt_regs, bx),
+	offsetof(struct pt_regs, sp),
+	offsetof(struct pt_regs, bp),
+	offsetof(struct pt_regs, si),
+	offsetof(struct pt_regs, di),
+#ifdef CONFIG_X86_64
+	offsetof(struct pt_regs, r8),
+	offsetof(struct pt_regs, r9),
+	offsetof(struct pt_regs, r10),
+	offsetof(struct pt_regs, r11),
+	offsetof(struct pt_regs, r12),
+	offsetof(struct pt_regs, r13),
+	offsetof(struct pt_regs, r14),
+	offsetof(struct pt_regs, r15),
+#endif
+};
+
+int pt_regs_offset(struct pt_regs *regs, int regno)
 {
+	if ((unsigned)regno < ARRAY_SIZE(pt_regoff))
+		return pt_regoff[regno];
+	return -EDOM;
+}
+
+static int get_regno(struct insn *insn, enum reg_type type)
+{
+	int nr_registers = ARRAY_SIZE(pt_regoff);
 	int regno = 0;
 
-	static const int regoff[] = {
-		offsetof(struct pt_regs, ax),
-		offsetof(struct pt_regs, cx),
-		offsetof(struct pt_regs, dx),
-		offsetof(struct pt_regs, bx),
-		offsetof(struct pt_regs, sp),
-		offsetof(struct pt_regs, bp),
-		offsetof(struct pt_regs, si),
-		offsetof(struct pt_regs, di),
-#ifdef CONFIG_X86_64
-		offsetof(struct pt_regs, r8),
-		offsetof(struct pt_regs, r9),
-		offsetof(struct pt_regs, r10),
-		offsetof(struct pt_regs, r11),
-		offsetof(struct pt_regs, r12),
-		offsetof(struct pt_regs, r13),
-		offsetof(struct pt_regs, r14),
-		offsetof(struct pt_regs, r15),
-#endif
-	};
-	int nr_registers = ARRAY_SIZE(regoff);
 	/*
 	 * Don't possibly decode a 32-bit instructions as
 	 * reading a 64-bit-only register.
@@ -505,7 +512,18 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 		WARN_ONCE(1, "decoded an instruction with an invalid register");
 		return -EINVAL;
 	}
-	return regoff[regno];
+	return regno;
+}
+
+static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
+			  enum reg_type type)
+{
+	int regno = get_regno(insn, type);
+
+	if (regno < 0)
+		return regno;
+
+	return pt_regs_offset(regs, regno);
 }
 
 /**