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arm64: extable: add `type` and `data` fields 

Subsequent patches will add specialized handlers for fixups, in addition
to the simple PC fixup and BPF handlers we have today. In preparation,
this patch adds a new `type` field to struct exception_table_entry, and
uses this to distinguish the fixup and BPF cases. A `data` field is also
added so that subsequent patches can associate data specific to each
exception site (e.g. register numbers).

Handlers are named ex_handler_*() for consistency, following the exmaple
of x86. At the same time, get_ex_fixup() is split out into a helper so
that it can be used by other ex_handler_*() functions ins subsequent
patches.

This patch will increase the size of the exception tables, which will be
remedied by subsequent patches removing redundant fixup code. There
should be no functional change as a result of this patch.

Since each entry is now 12 bytes in size, we must reduce the alignment
of each entry from `.align 3` (i.e. 8 bytes) to `.align 2` (i.e. 4
bytes), which is the natrual alignment of the `insn` and `fixup` fields.
The current 8-byte alignment is a holdover from when the `insn` and
`fixup` fields was 8 bytes, and while not harmful has not been necessary
since commit:

  6c94f27ac8 ("arm64: switch to relative exception tables")

Similarly, RO_EXCEPTION_TABLE_ALIGN is dropped to 4 bytes.

Concurrently with this patch, x86's exception table entry format is
being updated (similarly to a 12-byte format, with 32-bytes of absolute
data). Once both have been merged it should be possible to unify the
sorttable logic for the two.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: James Morse <james.morse@arm.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20211019160219.5202-11-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2021-10-19 17:02:16 +01:00 committed by Will Deacon
parent 5d0e790514
commit d6e2cc5647
6 changed files with 96 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
arch/arm64/include/asm/asm-extable.h
View File

@ -2,13 +2,19 @@
#ifndef __ASM_ASM_EXTABLE_H
#define __ASM_ASM_EXTABLE_H
#define EX_TYPE_NONE 0
#define EX_TYPE_FIXUP 1
#define EX_TYPE_BPF 2
#ifdef __ASSEMBLY__
#define __ASM_EXTABLE_RAW(insn, fixup) \
.pushsection __ex_table, "a"; \
.align 3; \
.long ((insn) - .); \
.long ((fixup) - .); \
#define __ASM_EXTABLE_RAW(insn, fixup, type, data) \
.pushsection __ex_table, "a"; \
.align 2; \
.long ((insn) - .); \
.long ((fixup) - .); \
.short (type); \
.short (data); \
.popsection;
/*
@ -16,7 +22,7 @@
* when an unhandled fault is taken.
*/
.macro _asm_extable, insn, fixup
__ASM_EXTABLE_RAW(\insn, \fixup)
__ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
.endm
/*
@ -33,15 +39,17 @@
#include <linux/stringify.h>
#define __ASM_EXTABLE_RAW(insn, fixup) \
".pushsection __ex_table, \"a\"\n" \
".align 3\n" \
".long ((" insn ") - .)\n" \
".long ((" fixup ") - .)\n" \
#define __ASM_EXTABLE_RAW(insn, fixup, type, data) \
".pushsection __ex_table, \"a\"\n" \
".align 2\n" \
".long ((" insn ") - .)\n" \
".long ((" fixup ") - .)\n" \
".short (" type ")\n" \
".short (" data ")\n" \
".popsection\n"
#define _ASM_EXTABLE(insn, fixup) \
__ASM_EXTABLE_RAW(#insn, #fixup)
__ASM_EXTABLE_RAW(#insn, #fixup, __stringify(EX_TYPE_FIXUP), "0")
#endif /* __ASSEMBLY__ */

19
arch/arm64/include/asm/extable.h
View File

@ -18,10 +18,21 @@
struct exception_table_entry
{
int insn, fixup;
short type, data;
};
#define ARCH_HAS_RELATIVE_EXTABLE
#define swap_ex_entry_fixup(a, b, tmp, delta) \
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)
static inline bool in_bpf_jit(struct pt_regs *regs)
{
if (!IS_ENABLED(CONFIG_BPF_JIT))
@ -32,12 +43,12 @@ static inline bool in_bpf_jit(struct pt_regs *regs)
}
#ifdef CONFIG_BPF_JIT
bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex,
struct pt_regs *regs);
bool ex_handler_bpf(const struct exception_table_entry *ex,
struct pt_regs *regs);
#else /* !CONFIG_BPF_JIT */
static inline
bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex,
struct pt_regs *regs)
bool ex_handler_bpf(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
return false;
}

2
arch/arm64/kernel/vmlinux.lds.S
View File

@ -57,7 +57,7 @@
#define SBSS_ALIGN 0
#endif
#define RO_EXCEPTION_TABLE_ALIGN 8
#define RO_EXCEPTION_TABLE_ALIGN 4
#define RUNTIME_DISCARD_EXIT
#include <asm-generic/vmlinux.lds.h>

29
arch/arm64/mm/extable.c
View File

@ -6,6 +6,24 @@
#include <linux/extable.h>
#include <linux/uaccess.h>
#include <asm/asm-extable.h>
typedef bool (*ex_handler_t)(const struct exception_table_entry *,
struct pt_regs *);
static inline unsigned long
get_ex_fixup(const struct exception_table_entry *ex)
{
return ((unsigned long)&ex->fixup + ex->fixup);
}
static bool ex_handler_fixup(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
regs->pc = get_ex_fixup(ex);
return true;
}
bool fixup_exception(struct pt_regs *regs)
{
const struct exception_table_entry *ex;
@ -14,9 +32,12 @@ bool fixup_exception(struct pt_regs *regs)
if (!ex)
return false;
if (in_bpf_jit(regs))
return arm64_bpf_fixup_exception(ex, regs);
switch (ex->type) {
case EX_TYPE_FIXUP:
return ex_handler_fixup(ex, regs);
case EX_TYPE_BPF:
return ex_handler_bpf(ex, regs);
}
regs->pc = (unsigned long)&ex->fixup + ex->fixup;
return true;
BUG();
}

7
arch/arm64/net/bpf_jit_comp.c
View File

@ -13,6 +13,7 @@
#include <linux/printk.h>
#include <linux/slab.h>
#include <asm/asm-extable.h>
#include <asm/byteorder.h>
#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
@ -358,8 +359,8 @@ static void build_epilogue(struct jit_ctx *ctx)
#define BPF_FIXUP_OFFSET_MASK GENMASK(26, 0)
#define BPF_FIXUP_REG_MASK GENMASK(31, 27)
bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex,
struct pt_regs *regs)
bool ex_handler_bpf(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
off_t offset = FIELD_GET(BPF_FIXUP_OFFSET_MASK, ex->fixup);
int dst_reg = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup);
@ -412,6 +413,8 @@ static int add_exception_handler(const struct bpf_insn *insn,
ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, offset) |
FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
ex->type = EX_TYPE_BPF;
ctx->exentry_idx++;
return 0;
}

30
scripts/sorttable.c
View File

@ -231,6 +231,34 @@ static void sort_relative_table(char *extab_image, int image_size)
}
}
static void arm64_sort_relative_table(char *extab_image, int image_size)
{
int i = 0;
while (i < image_size) {
uint32_t *loc = (uint32_t *)(extab_image + i);
w(r(loc) + i, loc);
w(r(loc + 1) + i + 4, loc + 1);
/* Don't touch the fixup type or data */
i += sizeof(uint32_t) * 3;
}
qsort(extab_image, image_size / 12, 12, compare_relative_table);
i = 0;
while (i < image_size) {
uint32_t *loc = (uint32_t *)(extab_image + i);
w(r(loc) - i, loc);
w(r(loc + 1) - (i + 4), loc + 1);
/* Don't touch the fixup type or data */
i += sizeof(uint32_t) * 3;
}
}
static void x86_sort_relative_table(char *extab_image, int image_size)
{
int i = 0;
@ -343,6 +371,8 @@ static int do_file(char const *const fname, void *addr)
custom_sort = s390_sort_relative_table;
break;
case EM_AARCH64:
custom_sort = arm64_sort_relative_table;
break;
case EM_PARISC:
case EM_PPC:
case EM_PPC64: