arm64: switch to relative exception tables
Instead of using absolute addresses for both the exception location
and the fixup, use offsets relative to the exception table entry values.
Not only does this cut the size of the exception table in half, it is
also a prerequisite for KASLR, since absolute exception table entries
are subject to dynamic relocation, which is incompatible with the sorting
of the exception table that occurs at build time.
This patch also introduces the _ASM_EXTABLE preprocessor macro (which
exists on x86 as well) and its _asm_extable assembly counterpart, as
shorthands to emit exception table entries.
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index a9fc24e..beccbde 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -157,11 +157,8 @@
add \addr, \addr, \post_inc;
alternative_endif
- .section __ex_table,"a";
- .align 3;
- .quad 8888b,\l;
- .quad 8889b,\l;
- .previous;
+ _asm_extable 8888b,\l;
+ _asm_extable 8889b,\l;
.endm
.macro uao_stp l, reg1, reg2, addr, post_inc
@@ -175,11 +172,8 @@
add \addr, \addr, \post_inc;
alternative_endif
- .section __ex_table,"a";
- .align 3;
- .quad 8888b,\l;
- .quad 8889b,\l;
- .previous
+ _asm_extable 8888b,\l;
+ _asm_extable 8889b,\l;
.endm
.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
@@ -191,10 +185,7 @@
add \addr, \addr, \post_inc;
alternative_endif
- .section __ex_table,"a";
- .align 3;
- .quad 8888b,\l;
- .previous
+ _asm_extable 8888b,\l;
.endm
#else
.macro uao_ldp l, reg1, reg2, addr, post_inc
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ba5aff6..70f7b9e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -94,12 +94,19 @@
dmb \opt
.endm
+/*
+ * Emit an entry into the exception table
+ */
+ .macro _asm_extable, from, to
+ .pushsection __ex_table, "a"
+ .align 3
+ .long (\from - .), (\to - .)
+ .popsection
+ .endm
+
#define USER(l, x...) \
9999: x; \
- .section __ex_table,"a"; \
- .align 3; \
- .quad 9999b,l; \
- .previous
+ _asm_extable 9999b, l
/*
* Register aliases.
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 5f3ab8c..f2585cd 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -42,10 +42,8 @@
"4: mov %w0, %w5\n" \
" b 3b\n" \
" .popsection\n" \
-" .pushsection __ex_table,\"a\"\n" \
-" .align 3\n" \
-" .quad 1b, 4b, 2b, 4b\n" \
-" .popsection\n" \
+ _ASM_EXTABLE(1b, 4b) \
+ _ASM_EXTABLE(2b, 4b) \
ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN, \
CONFIG_ARM64_PAN) \
: "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp) \
@@ -134,10 +132,8 @@
"4: mov %w0, %w6\n"
" b 3b\n"
" .popsection\n"
-" .pushsection __ex_table,\"a\"\n"
-" .align 3\n"
-" .quad 1b, 4b, 2b, 4b\n"
-" .popsection\n"
+ _ASM_EXTABLE(1b, 4b)
+ _ASM_EXTABLE(2b, 4b)
ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
: "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp)
: "r" (oldval), "r" (newval), "Ir" (-EFAULT)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 16ba0d5..0685d74 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -36,11 +36,11 @@
#define VERIFY_WRITE 1
/*
- * The exception table consists of pairs of addresses: the first is the
- * address of an instruction that is allowed to fault, and the second is
- * the address at which the program should continue. No registers are
- * modified, so it is entirely up to the continuation code to figure out
- * what to do.
+ * The exception table consists of pairs of relative offsets: the first
+ * is the relative offset to an instruction that is allowed to fault,
+ * and the second is the relative offset at which the program should
+ * continue. No registers are modified, so it is entirely up to the
+ * continuation code to figure out what to do.
*
* All the routines below use bits of fixup code that are out of line
* with the main instruction path. This means when everything is well,
@@ -50,9 +50,11 @@
struct exception_table_entry
{
- unsigned long insn, fixup;
+ int insn, fixup;
};
+#define ARCH_HAS_RELATIVE_EXTABLE
+
extern int fixup_exception(struct pt_regs *regs);
#define KERNEL_DS (-1UL)
@@ -115,6 +117,12 @@
#define access_ok(type, addr, size) __range_ok(addr, size)
#define user_addr_max get_fs
+#define _ASM_EXTABLE(from, to) \
+ " .pushsection __ex_table, \"a\"\n" \
+ " .align 3\n" \
+ " .long (" #from " - .), (" #to " - .)\n" \
+ " .popsection\n"
+
/*
* The "__xxx" versions of the user access functions do not verify the address
* space - it must have been done previously with a separate "access_ok()"
@@ -134,10 +142,7 @@
" mov %1, #0\n" \
" b 2b\n" \
" .previous\n" \
- " .section __ex_table,\"a\"\n" \
- " .align 3\n" \
- " .quad 1b, 3b\n" \
- " .previous" \
+ _ASM_EXTABLE(1b, 3b) \
: "+r" (err), "=&r" (x) \
: "r" (addr), "i" (-EFAULT))
@@ -206,10 +211,7 @@
"3: mov %w0, %3\n" \
" b 2b\n" \
" .previous\n" \
- " .section __ex_table,\"a\"\n" \
- " .align 3\n" \
- " .quad 1b, 3b\n" \
- " .previous" \
+ _ASM_EXTABLE(1b, 3b) \
: "+r" (err) \
: "r" (x), "r" (addr), "i" (-EFAULT))
diff --git a/arch/arm64/include/asm/word-at-a-time.h b/arch/arm64/include/asm/word-at-a-time.h
index aab5bf0..2b79b8a 100644
--- a/arch/arm64/include/asm/word-at-a-time.h
+++ b/arch/arm64/include/asm/word-at-a-time.h
@@ -16,6 +16,8 @@
#ifndef __ASM_WORD_AT_A_TIME_H
#define __ASM_WORD_AT_A_TIME_H
+#include <asm/uaccess.h>
+
#ifndef __AARCH64EB__
#include <linux/kernel.h>
@@ -81,10 +83,7 @@
#endif
" b 2b\n"
" .popsection\n"
- " .pushsection __ex_table,\"a\"\n"
- " .align 3\n"
- " .quad 1b, 3b\n"
- " .popsection"
+ _ASM_EXTABLE(1b, 3b)
: "=&r" (ret), "=&r" (offset)
: "r" (addr), "Q" (*(unsigned long *)addr));