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arm64: switch to relative exception tables

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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>
This commit is contained in:
Ard Biesheuvel
2016-01-01 15:02:12 +01:00
committed by Catalin Marinas
parent a272858a3c
commit 6c94f27ac8
8 changed files with 43 additions and 51 deletions
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30
arch/arm64/include/asm/uaccess.h
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@@ -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 @@ static inline void set_fs(mm_segment_t fs)
#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 @@ static inline void set_fs(mm_segment_t fs)
" 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 @@ do { \
"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))