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Message-ID: <CAJcbSZEd10fMp6OSgSYv_Wmt=wX5fw_Gu-_N=fM_QmP==wUMew@mail.gmail.com>
Date: Tue, 29 Aug 2017 07:32:39 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Al Viro <viro@...iv.linux.org.uk>, Dave Hansen <dave.hansen@...el.com>,
Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>, Thomas Garnier <thgarnie@...gle.com>,
Yonghong Song <yhs@...com>, David Howells <dhowells@...hat.com>, Russell King <linux@...linux.org.uk>,
Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...capital.net>,
Will Drewry <wad@...omium.org>, Dave Martin <Dave.Martin@....com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>
Cc: Linux API <linux-api@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Lothar Waßmann <LW@...o-electronics.de>
Subject: Re: [PATCH v3 3/4] arm/syscalls: Optimize address limit check
On Tue, Aug 22, 2017 at 9:42 AM, Thomas Garnier <thgarnie@...gle.com> wrote:
> On Mon, Aug 14, 2017 at 2:37 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
>> Disable the generic address limit check in favor of an architecture
>> specific optimized implementation. The generic implementation using
>> pending work flags did not work well with ARM and alignment faults.
>>
>> The address limit is checked on each syscall return path to user-mode
>> path as well as the irq user-mode return function. If the address limit
>> was changed, a function is called to report data corruption (stopping
>> the kernel or process based on configuration).
>>
>> The address limit check has to be done before any pending work because
>> they can reset the address limit and the process is killed using a
>> SIGKILL signal. For example the lkdtm address limit check does not work
>> because the signal to kill the process will reset the user-mode address
>> limit.
>>
>> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>
> Any feedback?
CCing LW@...o-electronics.de who experienced the same issue this patch
proposal fix.
Russel: Any feedback?
>
>> ---
>> arch/arm/kernel/entry-common.S | 11 +++++++++++
>> arch/arm/kernel/signal.c | 7 +++++++
>> 2 files changed, 18 insertions(+)
>>
>> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
>> index 0b60adf4a5d9..99c908226065 100644
>> --- a/arch/arm/kernel/entry-common.S
>> +++ b/arch/arm/kernel/entry-common.S
>> @@ -12,6 +12,7 @@
>> #include <asm/unistd.h>
>> #include <asm/ftrace.h>
>> #include <asm/unwind.h>
>> +#include <asm/memory.h>
>> #ifdef CONFIG_AEABI
>> #include <asm/unistd-oabi.h>
>> #endif
>> @@ -48,10 +49,14 @@ ret_fast_syscall:
>> UNWIND(.fnstart )
>> UNWIND(.cantunwind )
>> disable_irq_notrace @ disable interrupts
>> + ldr r2, [tsk, #TI_ADDR_LIMIT]
>> + cmp r2, #TASK_SIZE
>> + blne addr_limit_check_failed
>> ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
>> tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
>> bne fast_work_pending
>>
>> +
>> /* perform architecture specific actions before user return */
>> arch_ret_to_user r1, lr
>>
>> @@ -74,6 +79,9 @@ ret_fast_syscall:
>> UNWIND(.cantunwind )
>> str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
>> disable_irq_notrace @ disable interrupts
>> + ldr r2, [tsk, #TI_ADDR_LIMIT]
>> + cmp r2, #TASK_SIZE
>> + blne addr_limit_check_failed
>> ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
>> tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
>> beq no_work_pending
>> @@ -106,6 +114,9 @@ ENTRY(ret_to_user)
>> ret_slow_syscall:
>> disable_irq_notrace @ disable interrupts
>> ENTRY(ret_to_user_from_irq)
>> + ldr r2, [tsk, #TI_ADDR_LIMIT]
>> + cmp r2, #TASK_SIZE
>> + blne addr_limit_check_failed
>> ldr r1, [tsk, #TI_FLAGS]
>> tst r1, #_TIF_WORK_MASK
>> bne slow_work_pending
>> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
>> index 5814298ef0b7..b67ae12503f3 100644
>> --- a/arch/arm/kernel/signal.c
>> +++ b/arch/arm/kernel/signal.c
>> @@ -14,6 +14,7 @@
>> #include <linux/uaccess.h>
>> #include <linux/tracehook.h>
>> #include <linux/uprobes.h>
>> +#include <linux/syscalls.h>
>>
>> #include <asm/elf.h>
>> #include <asm/cacheflush.h>
>> @@ -673,3 +674,9 @@ struct page *get_signal_page(void)
>>
>> return page;
>> }
>> +
>> +/* Defer to generic check */
>> +asmlinkage void addr_limit_check_failed(void)
>> +{
>> + addr_limit_user_check();
>> +}
>> --
>> 2.14.1.480.gb18f417b89-goog
>>
>
>
>
> --
> Thomas
--
Thomas
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