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.
Change-Id: I2c5198c7400f721117c9366c96e847c49213a516
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>
Git-commit: c02433dd6de32f042cf3ffe476746b1115b8c096
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[ohaugan@codeaurora.org: Fix merge conflicts related to SW PAN]
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c6c41ab..718c4c8 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -93,9 +93,8 @@
.if \el == 0
mrs x21, sp_el0
- mov tsk, sp
- and tsk, tsk, #~(THREAD_SIZE - 1) // Ensure MDSCR_EL1.SS is clear,
- ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug
+ ldr_this_cpu tsk, __entry_task, x20 // Ensure MDSCR_EL1.SS is clear,
+ ldr x19, [tsk, #TSK_TI_FLAGS] // since we can unmask debug
disable_step_tsk x19, x20 // exceptions when scheduling.
mov x29, xzr // fp pointed to user-space
@@ -103,10 +102,10 @@
add x21, sp, #S_FRAME_SIZE
get_thread_info tsk
/* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */
- ldr x20, [tsk, #TI_ADDR_LIMIT]
+ ldr x20, [tsk, #TSK_TI_ADDR_LIMIT]
str x20, [sp, #S_ORIG_ADDR_LIMIT]
mov x20, #TASK_SIZE_64
- str x20, [tsk, #TI_ADDR_LIMIT]
+ str x20, [tsk, #TSK_TI_ADDR_LIMIT]
/* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */
.endif /* \el == 0 */
mrs x22, elr_el1
@@ -168,7 +167,7 @@
.if \el != 0
/* Restore the task's original addr_limit. */
ldr x20, [sp, #S_ORIG_ADDR_LIMIT]
- str x20, [tsk, #TI_ADDR_LIMIT]
+ str x20, [tsk, #TSK_TI_ADDR_LIMIT]
/* No need to restore UAO, it will be restored from SPSR_EL1 */
.endif
@@ -252,13 +251,14 @@
mov x19, sp // preserve the original sp
/*
- * Compare sp with the current thread_info, if the top
- * ~(THREAD_SIZE - 1) bits match, we are on a task stack, and
- * should switch to the irq stack.
+ * Compare sp with the base of the task stack.
+ * If the top ~(THREAD_SIZE - 1) bits match, we are on a task stack,
+ * and should switch to the irq stack.
*/
- and x25, x19, #~(THREAD_SIZE - 1)
- cmp x25, tsk
- b.ne 9998f
+ ldr x25, [tsk, TSK_STACK]
+ eor x25, x25, x19
+ and x25, x25, #~(THREAD_SIZE - 1)
+ cbnz x25, 9998f
adr_this_cpu x25, irq_stack, x26
mov x26, #IRQ_STACK_START_SP
@@ -488,9 +488,9 @@
irq_handler
#ifdef CONFIG_PREEMPT
- ldr w24, [tsk, #TI_PREEMPT] // get preempt count
+ ldr w24, [tsk, #TSK_TI_PREEMPT] // get preempt count
cbnz w24, 1f // preempt count != 0
- ldr x0, [tsk, #TI_FLAGS] // get flags
+ ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
bl el1_preempt
1:
@@ -505,7 +505,7 @@
el1_preempt:
mov x24, lr
1: bl preempt_schedule_irq // irq en/disable is done inside
- ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS
+ ldr x0, [tsk, #TSK_TI_FLAGS] // get new tasks TI_FLAGS
tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling?
ret x24
#endif
@@ -735,8 +735,7 @@
ldp x29, x9, [x8], #16
ldr lr, [x8]
mov sp, x9
- and x9, x9, #~(THREAD_SIZE - 1)
- msr sp_el0, x9
+ msr sp_el0, x1
ret
ENDPROC(cpu_switch_to)
@@ -747,7 +746,7 @@
ret_fast_syscall:
disable_irq // disable interrupts
str x0, [sp, #S_X0] // returned x0
- ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing
+ ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
and x2, x1, #_TIF_WORK_MASK
@@ -767,14 +766,14 @@
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_on // enabled while in userspace
#endif
- ldr x1, [tsk, #TI_FLAGS] // re-check for single-step
+ ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for single-step
b finish_ret_to_user
/*
* "slow" syscall return path.
*/
ret_to_user:
disable_irq // disable interrupts
- ldr x1, [tsk, #TI_FLAGS]
+ ldr x1, [tsk, #TSK_TI_FLAGS]
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
finish_ret_to_user:
@@ -807,7 +806,7 @@
enable_dbg_and_irq
ct_user_exit 1
- ldr x16, [tsk, #TI_FLAGS] // check for syscall hooks
+ ldr x16, [tsk, #TSK_TI_FLAGS] // check for syscall hooks
tst x16, #_TIF_SYSCALL_WORK
b.ne __sys_trace
cmp scno, sc_nr // check upper syscall limit