Commit e33f8d32 authored Sep 07, 2017 by Thomas Garnier Committed by Thomas Gleixner Sep 17, 2017

arm/syscalls: Optimize address limit check



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@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: Will Drewry <wad@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-api@vger.kernel.org
Cc: Yonghong Song <yhs@fb.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1504798247-48833-4-git-send-email-keescook@chromium.org

parent 2404269b

arch/arm/kernel/entry-common.S

+11 −0

Original line number	Diff line number	Diff line
		@@ -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

arch/arm/kernel/signal.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -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();
		}

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