arm64: split thread_info from task stack
authorMark Rutland <mark.rutland@arm.com>
Thu, 3 Nov 2016 20:23:13 +0000 (20:23 +0000)
committerCatalin Marinas <catalin.marinas@arm.com>
Fri, 11 Nov 2016 18:25:46 +0000 (18:25 +0000)
commitc02433dd6de32f042cf3ffe476746b1115b8c096
tree265e0b7925a4c665a64b5f8d4279d16dcb947ee2
parent1b7e2296a822dfd2349960addc42a139360ce769
arm64: split thread_info from task stack

This patch moves arm64's struct thread_info from the task stack into
task_struct. This protects thread_info from corruption in the case of
stack overflows, and makes its address harder to determine if stack
addresses are leaked, making a number of attacks more difficult. Precise
detection and handling of overflow is left for subsequent patches.

Largely, this involves changing code to store the task_struct in sp_el0,
and acquire the thread_info from the task struct. Core code now
implements current_thread_info(), and as noted in <linux/sched.h> this
relies on offsetof(task_struct, thread_info) == 0, enforced by core
code.

This change means that the 'tsk' register used in entry.S now points to
a task_struct, rather than a thread_info as it used to. To make this
clear, the TI_* field offsets are renamed to TSK_TI_*, with asm-offsets
appropriately updated to account for the structural change.

Userspace clobbers sp_el0, and we can no longer restore this from the
stack. Instead, the current task is cached in a per-cpu variable that we
can safely access from early assembly as interrupts are disabled (and we
are thus not preemptible).

Both secondary entry and idle are updated to stash the sp and task
pointer separately.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arch/arm64/Kconfig
arch/arm64/include/asm/Kbuild
arch/arm64/include/asm/current.h [new file with mode: 0644]
arch/arm64/include/asm/smp.h
arch/arm64/include/asm/thread_info.h
arch/arm64/kernel/asm-offsets.c
arch/arm64/kernel/entry.S
arch/arm64/kernel/head.S
arch/arm64/kernel/process.c
arch/arm64/kernel/smp.c