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

4 files changed, 66 insertions, 3 deletions

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 3a168483bc8e..c878fed3056f 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -152,6 +152,33 @@
 
 #else /* ! __ASSEMBLY__ */
 
+# define DEFINE_EXTABLE_TYPE_REG \
+	".macro extable_type_reg type:req reg:req\n"						\
+	".set found, 0\n"									\
+	".set regnr, 0\n"									\
+	".irp rs,rax,rcx,rdx,rbx,rsp,rbp,rsi,rdi,r8,r9,r10,r11,r12,r13,r14,r15\n"		\
+	".ifc \\reg, %%\\rs\n"									\
+	".set found, found+1\n"									\
+	".long \\type + (regnr << 8)\n"								\
+	".endif\n"										\
+	".set regnr, regnr+1\n"									\
+	".endr\n"										\
+	".set regnr, 0\n"									\
+	".irp rs,eax,ecx,edx,ebx,esp,ebp,esi,edi,r8d,r9d,r10d,r11d,r12d,r13d,r14d,r15d\n"	\
+	".ifc \\reg, %%\\rs\n"									\
+	".set found, found+1\n"									\
+	".long \\type + (regnr << 8)\n"								\
+	".endif\n"										\
+	".set regnr, regnr+1\n"									\
+	".endr\n"										\
+	".if (found != 1)\n"									\
+	".error \"extable_type_reg: bad register argument\"\n"					\
+	".endif\n"										\
+	".endm\n"
+
+# define UNDEFINE_EXTABLE_TYPE_REG \
+	".purgem extable_type_reg\n"
+
 # define _ASM_EXTABLE_TYPE(from, to, type)			\
 	" .pushsection \"__ex_table\",\"a\"\n"			\
 	" .balign 4\n"						\
@@ -160,6 +187,16 @@
 	" .long " __stringify(type) " \n"			\
 	" .popsection\n"
 
+# define _ASM_EXTABLE_TYPE_REG(from, to, type, reg)				\
+	" .pushsection \"__ex_table\",\"a\"\n"					\
+	" .balign 4\n"								\
+	" .long (" #from ") - .\n"						\
+	" .long (" #to ") - .\n"						\
+	DEFINE_EXTABLE_TYPE_REG							\
+	"extable_type_reg reg=" __stringify(reg) ", type=" __stringify(type) " \n"\
+	UNDEFINE_EXTABLE_TYPE_REG						\
+	" .popsection\n"
+
 /* For C file, we already have NOKPROBE_SYMBOL macro */
 
 /*
diff --git a/arch/x86/include/asm/extable.h b/arch/x86/include/asm/extable.h
index 93f400eb728f..155c991ba95e 100644
--- a/arch/x86/include/asm/extable.h
+++ b/arch/x86/include/asm/extable.h
@@ -21,7 +21,7 @@
  */
 
 struct exception_table_entry {
-	int insn, fixup, type;
+	int insn, fixup, data;
 };
 struct pt_regs;
 
@@ -31,8 +31,8 @@ struct pt_regs;
 	do {							\
 		(a)->fixup = (b)->fixup + (delta);		\
 		(b)->fixup = (tmp).fixup - (delta);		\
-		(a)->type = (b)->type;				\
-		(b)->type = (tmp).type;				\
+		(a)->data = (b)->data;				\
+		(b)->data = (tmp).data;				\
 	} while (0)
 
 extern int fixup_exception(struct pt_regs *regs, int trapnr,
diff --git a/arch/x86/include/asm/extable_fixup_types.h b/arch/x86/include/asm/extable_fixup_types.h
index 4d709a2768bb..944f8329022a 100644
--- a/arch/x86/include/asm/extable_fixup_types.h
+++ b/arch/x86/include/asm/extable_fixup_types.h
@@ -2,6 +2,29 @@
 #ifndef _ASM_X86_EXTABLE_FIXUP_TYPES_H
 #define _ASM_X86_EXTABLE_FIXUP_TYPES_H
 
+/*
+ * Our IMM is signed, as such it must live at the top end of the word. Also,
+ * since C99 hex constants are of ambigious type, force cast the mask to 'int'
+ * so that FIELD_GET() will DTRT and sign extend the value when it extracts it.
+ */
+#define EX_DATA_TYPE_MASK		((int)0x000000FF)
+#define EX_DATA_REG_MASK		((int)0x00000F00)
+#define EX_DATA_FLAG_MASK		((int)0x0000F000)
+#define EX_DATA_IMM_MASK		((int)0xFFFF0000)
+
+#define EX_DATA_REG_SHIFT		8
+#define EX_DATA_FLAG_SHIFT		12
+#define EX_DATA_IMM_SHIFT		16
+
+#define EX_DATA_FLAG(flag)		((flag) << EX_DATA_FLAG_SHIFT)
+#define EX_DATA_IMM(imm)		((imm) << EX_DATA_IMM_SHIFT)
+
+/* flags */
+#define EX_FLAG_CLEAR_AX		EX_DATA_FLAG(1)
+#define EX_FLAG_CLEAR_DX		EX_DATA_FLAG(2)
+#define EX_FLAG_CLEAR_AX_DX		EX_DATA_FLAG(3)
+
+/* types */
 #define	EX_TYPE_NONE			 0
 #define	EX_TYPE_DEFAULT			 1
 #define	EX_TYPE_FAULT			 2
@@ -20,5 +43,6 @@
 #define	EX_TYPE_FAULT_MCE_SAFE		13
 
 #define	EX_TYPE_POP_ZERO		14
+#define	EX_TYPE_IMM_REG			15 /* reg := (long)imm */
 
 #endif
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 4ec3613551e3..3df123f437c9 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -15,6 +15,8 @@
 #define INSN_CODE_SEG_OPND_SZ(params) (params & 0xf)
 #define INSN_CODE_SEG_PARAMS(oper_sz, addr_sz) (oper_sz | (addr_sz << 4))
 
+int pt_regs_offset(struct pt_regs *regs, int regno);
+
 bool insn_has_rep_prefix(struct insn *insn);
 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);