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Message-ID: <nycvar.YSQ.7.76.1709041311230.8603@knanqh.ubzr>
Date: Mon, 4 Sep 2017 13:17:40 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc: linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com,
Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>,
Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>,
Marc Zyngier <marc.zyngier@....com>, Mark Rutland <mark.rutland@....com>,
Tony Lindgren <tony@...mide.com>, Matt Fleming <matt@...eblueprint.co.uk>,
Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v2 16/29] ARM: kernel: switch to relative exception
tables
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> To avoid having to relocate the contents of extable entries at
> runtime when running with KASLR enabled, wire up the existing
> support for emitting them as relative references. This ensures
> these quantities are invariant under runtime relocation.
>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Could it be better to have a macro that encapsulates exception entries
e.g.:
.macro ex_entry insn fixup
.long \insn - ., \fixup - .
.endif
so that if ever this changes again or for whatever reason someone needs
absolute entries then this won't have to be done everywhere. The section
switch could be included in such a macro too. And it is so easy to
forget to do the "- ." when adding new entries.
> ---
> arch/arm/include/asm/Kbuild | 1 -
> arch/arm/include/asm/assembler.h | 6 +++---
> arch/arm/include/asm/extable.h | 19 +++++++++++++++++
> arch/arm/include/asm/futex.h | 2 +-
> arch/arm/include/asm/uaccess.h | 8 +++----
> arch/arm/include/asm/word-at-a-time.h | 2 +-
> arch/arm/kernel/entry-armv.S | 6 +++---
> arch/arm/kernel/swp_emulate.c | 4 ++--
> arch/arm/lib/backtrace.S | 8 +++----
> arch/arm/lib/getuser.S | 22 ++++++++++----------
> arch/arm/lib/putuser.S | 12 +++++------
> arch/arm/mm/alignment.c | 14 ++++++-------
> arch/arm/mm/extable.c | 2 +-
> arch/arm/nwfpe/entry.S | 2 +-
> scripts/sortextable.c | 2 +-
> 15 files changed, 64 insertions(+), 46 deletions(-)
>
> diff --git a/arch/arm/include/asm/Kbuild b/arch/arm/include/asm/Kbuild
> index 721ab5ecfb9b..f2d67fa34eb3 100644
> --- a/arch/arm/include/asm/Kbuild
> +++ b/arch/arm/include/asm/Kbuild
> @@ -3,7 +3,6 @@ generic-y += current.h
> generic-y += early_ioremap.h
> generic-y += emergency-restart.h
> generic-y += exec.h
> -generic-y += extable.h
> generic-y += irq_regs.h
> generic-y += kdebug.h
> generic-y += local.h
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index a0906c1fc65d..ae43859a9000 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -247,7 +247,7 @@
> 9999: x; \
> .pushsection __ex_table,"a"; \
> .align 3; \
> - .long 9999b,9001f; \
> + .long 9999b - ., 9001f - .; \
> .popsection
>
> #ifdef CONFIG_SMP
> @@ -383,7 +383,7 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
>
> .pushsection __ex_table,"a"
> .align 3
> - .long 9999b, \abort
> + .long 9999b - ., \abort - .
> .popsection
> .endm
>
> @@ -424,7 +424,7 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
>
> .pushsection __ex_table,"a"
> .align 3
> - .long 9999b, \abort
> + .long 9999b - ., \abort - .
> .popsection
> .endr
> .endm
> diff --git a/arch/arm/include/asm/extable.h b/arch/arm/include/asm/extable.h
> new file mode 100644
> index 000000000000..c85d1f4404b7
> --- /dev/null
> +++ b/arch/arm/include/asm/extable.h
> @@ -0,0 +1,19 @@
> +#ifndef __ASM_EXTABLE_H
> +#define __ASM_EXTABLE_H
> +
> +/*
> + * 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.
> + */
> +
> +struct exception_table_entry {
> + int insn, fixup;
> +};
> +
> +#define ARCH_HAS_RELATIVE_EXTABLE
> +
> +extern int fixup_exception(struct pt_regs *regs);
> +#endif
> diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
> index 6795368ad023..31760d0ab76b 100644
> --- a/arch/arm/include/asm/futex.h
> +++ b/arch/arm/include/asm/futex.h
> @@ -11,7 +11,7 @@
> "3:\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 4f, 2b, 4f\n" \
> + " .long 1b - ., 4f - ., 2b - ., 4f - .\n" \
> " .popsection\n" \
> " .pushsection .text.fixup,\"ax\"\n" \
> " .align 2\n" \
> diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
> index 0bf2347495f1..62b9bb7d991a 100644
> --- a/arch/arm/include/asm/uaccess.h
> +++ b/arch/arm/include/asm/uaccess.h
> @@ -295,7 +295,7 @@ do { \
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 3b\n" \
> + " .long 1b - ., 3b - .\n" \
> " .popsection" \
> : "+r" (err), "=&r" (x) \
> : "r" (addr), "i" (-EFAULT) \
> @@ -385,7 +385,7 @@ do { \
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 3b\n" \
> + " .long 1b - ., 3b - .\n" \
> " .popsection" \
> : "+r" (err) \
> : "r" (x), "r" (__pu_addr), "i" (-EFAULT) \
> @@ -435,8 +435,8 @@ do { \
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 4b\n" \
> - " .long 2b, 4b\n" \
> + " .long 1b - ., 4b - .\n" \
> + " .long 2b - ., 4b - .\n" \
> " .popsection" \
> : "+r" (err), "+r" (__pu_addr) \
> : "r" (x), "i" (-EFAULT) \
> diff --git a/arch/arm/include/asm/word-at-a-time.h b/arch/arm/include/asm/word-at-a-time.h
> index 5831dce4b51c..d433c686d9ca 100644
> --- a/arch/arm/include/asm/word-at-a-time.h
> +++ b/arch/arm/include/asm/word-at-a-time.h
> @@ -86,7 +86,7 @@ static inline unsigned long load_unaligned_zeropad(const void *addr)
> " .popsection\n"
> " .pushsection __ex_table,\"a\"\n"
> " .align 3\n"
> - " .long 1b, 3b\n"
> + " .long 1b - ., 3b - .\n"
> " .popsection"
> : "=&r" (ret), "=&r" (offset)
> : "r" (addr), "Qo" (*(unsigned long *)addr));
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index c731f0d2b2af..1c7c12123b18 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -570,10 +570,10 @@ ENDPROC(__und_usr)
> ret r9
> .popsection
> .pushsection __ex_table,"a"
> - .long 1b, 4b
> + .long 1b - ., 4b - .
> #if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7
> - .long 2b, 4b
> - .long 3b, 4b
> + .long 2b - ., 4b - .
> + .long 3b - ., 4b - .
> #endif
> .popsection
>
> diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
> index 3bda08bee674..a783e9c0b266 100644
> --- a/arch/arm/kernel/swp_emulate.c
> +++ b/arch/arm/kernel/swp_emulate.c
> @@ -50,8 +50,8 @@
> " .previous\n" \
> " .section __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 0b, 3b\n" \
> - " .long 1b, 3b\n" \
> + " .long 0b - ., 3b - .\n" \
> + " .long 1b - ., 3b - .\n" \
> " .previous" \
> : "=&r" (res), "+r" (data), "=&r" (temp) \
> : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
> diff --git a/arch/arm/lib/backtrace.S b/arch/arm/lib/backtrace.S
> index 7d7952e5a3b1..84a8df7aa63c 100644
> --- a/arch/arm/lib/backtrace.S
> +++ b/arch/arm/lib/backtrace.S
> @@ -107,10 +107,10 @@ ENDPROC(c_backtrace)
>
> .pushsection __ex_table,"a"
> .align 3
> - .long 1001b, 1006b
> - .long 1002b, 1006b
> - .long 1003b, 1006b
> - .long 1004b, 1006b
> + .long 1001b - ., 1006b - .
> + .long 1002b - ., 1006b - .
> + .long 1003b - ., 1006b - .
> + .long 1004b - ., 1006b - .
> .popsection
>
> .Lbad: .asciz "Backtrace aborted due to bad frame pointer <%p>\n"
> diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S
> index df73914e81c8..d47b4776d308 100644
> --- a/arch/arm/lib/getuser.S
> +++ b/arch/arm/lib/getuser.S
> @@ -133,17 +133,17 @@ ENDPROC(__get_user_bad)
> ENDPROC(__get_user_bad8)
>
> .pushsection __ex_table, "a"
> - .long 1b, __get_user_bad
> - .long 2b, __get_user_bad
> - .long 3b, __get_user_bad
> - .long 4b, __get_user_bad
> - .long 5b, __get_user_bad8
> - .long 6b, __get_user_bad8
> + .long 1b - ., __get_user_bad - .
> + .long 2b - ., __get_user_bad - .
> + .long 3b - ., __get_user_bad - .
> + .long 4b - ., __get_user_bad - .
> + .long 5b - ., __get_user_bad8 - .
> + .long 6b - ., __get_user_bad8 - .
> #ifdef __ARMEB__
> - .long 7b, __get_user_bad
> - .long 8b, __get_user_bad8
> - .long 9b, __get_user_bad8
> - .long 10b, __get_user_bad8
> - .long 11b, __get_user_bad8
> + .long 7b - ., __get_user_bad - .
> + .long 8b - ., __get_user_bad8 - .
> + .long 9b - ., __get_user_bad8 - .
> + .long 10b - ., __get_user_bad8 - .
> + .long 11b - ., __get_user_bad8 - .
> #endif
> .popsection
> diff --git a/arch/arm/lib/putuser.S b/arch/arm/lib/putuser.S
> index 38d660d3705f..6b854197ff48 100644
> --- a/arch/arm/lib/putuser.S
> +++ b/arch/arm/lib/putuser.S
> @@ -89,10 +89,10 @@ __put_user_bad:
> ENDPROC(__put_user_bad)
>
> .pushsection __ex_table, "a"
> - .long 1b, __put_user_bad
> - .long 2b, __put_user_bad
> - .long 3b, __put_user_bad
> - .long 4b, __put_user_bad
> - .long 5b, __put_user_bad
> - .long 6b, __put_user_bad
> + .long 1b - ., __put_user_bad - .
> + .long 2b - ., __put_user_bad - .
> + .long 3b - ., __put_user_bad - .
> + .long 4b - ., __put_user_bad - .
> + .long 5b - ., __put_user_bad - .
> + .long 6b - ., __put_user_bad - .
> .popsection
> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
> index 2c96190e018b..2c74cb826b6a 100644
> --- a/arch/arm/mm/alignment.c
> +++ b/arch/arm/mm/alignment.c
> @@ -209,7 +209,7 @@ union offset_union {
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 3b\n" \
> + " .long 1b - ., 3b - .\n" \
> " .popsection\n" \
> : "=r" (err), "=&r" (val), "=r" (addr) \
> : "0" (err), "2" (addr))
> @@ -269,8 +269,8 @@ union offset_union {
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 4b\n" \
> - " .long 2b, 4b\n" \
> + " .long 1b - ., 4b - .\n" \
> + " .long 2b - ., 4b - .\n" \
> " .popsection\n" \
> : "=r" (err), "=&r" (v), "=&r" (a) \
> : "0" (err), "1" (v), "2" (a)); \
> @@ -309,10 +309,10 @@ union offset_union {
> " .popsection\n" \
> " .pushsection __ex_table,\"a\"\n" \
> " .align 3\n" \
> - " .long 1b, 6b\n" \
> - " .long 2b, 6b\n" \
> - " .long 3b, 6b\n" \
> - " .long 4b, 6b\n" \
> + " .long 1b - ., 6b - .\n" \
> + " .long 2b - ., 6b - .\n" \
> + " .long 3b - ., 6b - .\n" \
> + " .long 4b - ., 6b - .\n" \
> " .popsection\n" \
> : "=r" (err), "=&r" (v), "=&r" (a) \
> : "0" (err), "1" (v), "2" (a)); \
> diff --git a/arch/arm/mm/extable.c b/arch/arm/mm/extable.c
> index f436f7439e46..6a8b85bf0cac 100644
> --- a/arch/arm/mm/extable.c
> +++ b/arch/arm/mm/extable.c
> @@ -10,7 +10,7 @@ int fixup_exception(struct pt_regs *regs)
>
> fixup = search_exception_tables(instruction_pointer(regs));
> if (fixup) {
> - regs->ARM_pc = fixup->fixup;
> + regs->ARM_pc = (unsigned long)&fixup->fixup + fixup->fixup;
> #ifdef CONFIG_THUMB2_KERNEL
> /* Clear the IT state to avoid nasty surprises in the fixup */
> regs->ARM_cpsr &= ~PSR_IT_MASK;
> diff --git a/arch/arm/nwfpe/entry.S b/arch/arm/nwfpe/entry.S
> index 39c20afad7ed..c4fe13b31705 100644
> --- a/arch/arm/nwfpe/entry.S
> +++ b/arch/arm/nwfpe/entry.S
> @@ -121,5 +121,5 @@ next:
>
> .pushsection __ex_table,"a"
> .align 3
> - .long .Lx1, .Lfix
> + .long .Lx1 - ., .Lfix - .
> .popsection
> diff --git a/scripts/sortextable.c b/scripts/sortextable.c
> index 365a907f98b3..56a4c6714da7 100644
> --- a/scripts/sortextable.c
> +++ b/scripts/sortextable.c
> @@ -314,6 +314,7 @@ do_file(char const *const fname)
> break;
>
> case EM_S390:
> + case EM_ARM:
> case EM_AARCH64:
> case EM_PARISC:
> case EM_PPC:
> @@ -322,7 +323,6 @@ do_file(char const *const fname)
> break;
> case EM_ARCOMPACT:
> case EM_ARCV2:
> - case EM_ARM:
> case EM_MICROBLAZE:
> case EM_MIPS:
> case EM_XTENSA:
> --
> 2.11.0
>
>
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