evie/android_kernel_oneplus_msm8998
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BACKPORT: arm64: split thread_info from task stack

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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>

This is a modification of Mark Rutland's original patch. Guards to check
if CONFIG_THREAD_INFO_IN_TASK is used has been inserted. get_current()
for when CONFIG_THREAD_INFO_IN_TASK is not used has been added to
arch/arm64/include/asm/current.h.

Bug: 38331309
Change-Id: Ic5eae344a7c2baea0864f6ae16be1e9c60c0a74a
(cherry picked from commit c02433dd6de32f042cf3ffe476746b1115b8c096)
Signed-off-by: Zubin Mithra <zsm@google.com>
This commit is contained in:
Mark Rutland 2016-11-03 20:23:13 +00:00 • committed by Zubin Mithra
parent 1cdfc007f3
commit 4ca3c2cf00
9 changed files with 156 additions and 9 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
arch/arm64/Kconfig
View file

@ -98,6 +98,7 @@ config ARM64
select SPARSE_IRQ
select SYSCTL_EXCEPTION_TRACE
select HAVE_CONTEXT_TRACKING
select THREAD_INFO_IN_TASK
help
ARM 64-bit (AArch64) Linux support.

27
arch/arm64/include/asm/current.h Normal file
View file

@ -0,0 +1,27 @@
#ifndef __ASM_CURRENT_H
#define __ASM_CURRENT_H
#include <linux/compiler.h>
#include <asm/sysreg.h>
#ifndef __ASSEMBLY__
#ifdef CONFIG_THREAD_INFO_IN_TASK
struct task_struct;
static __always_inline struct task_struct *get_current(void)
{
return (struct task_struct *)read_sysreg(sp_el0);
}
#define current get_current()
#else
#include <linux/thread_info.h>
#define get_current() (current_thread_info()->task)
#define current get_current()
#endif
#endif /* __ASSEMBLY__ */
#endif /* __ASM_CURRENT_H */

3
arch/arm64/include/asm/smp.h
View file

@ -66,6 +66,9 @@ asmlinkage void secondary_start_kernel(void);
*/
struct secondary_data {
void *stack;
#ifdef CONFIG_THREAD_INFO_IN_TASK
struct task_struct *task;
#endif
};
extern struct secondary_data secondary_data;
extern void secondary_entry(void);

16
arch/arm64/include/asm/thread_info.h
View file

@ -47,14 +47,25 @@ typedef unsigned long mm_segment_t;
struct thread_info {
unsigned long flags; /* low level flags */
mm_segment_t addr_limit; /* address limit */
#ifndef CONFIG_THREAD_INFO_IN_TASK
struct task_struct *task; /* main task structure */
#endif
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
u64 ttbr0; /* saved TTBR0_EL1 */
#endif
int preempt_count; /* 0 => preemptable, <0 => bug */
#ifndef CONFIG_THREAD_INFO_IN_TASK
int cpu; /* cpu */
#endif
};
#ifdef CONFIG_THREAD_INFO_IN_TASK
#define INIT_THREAD_INFO(tsk) \
{ \
.preempt_count = INIT_PREEMPT_COUNT, \
.addr_limit = KERNEL_DS, \
}
#else
#define INIT_THREAD_INFO(tsk) \
{ \
.task = &tsk, \
@ -63,8 +74,6 @@ struct thread_info {
.addr_limit = KERNEL_DS, \
}
#define init_stack (init_thread_union.stack)
/*
* how to get the thread information struct from C
*/
@ -81,6 +90,9 @@ static inline struct thread_info *current_thread_info(void)
return (struct thread_info *)sp_el0;
}
#endif
#define init_stack (init_thread_union.stack)
#define thread_saved_pc(tsk) \
((unsigned long)(tsk->thread.cpu_context.pc))

14
arch/arm64/kernel/asm-offsets.c
View file

@ -33,12 +33,15 @@ int main(void)
{
DEFINE(TSK_ACTIVE_MM, offsetof(struct task_struct, active_mm));
BLANK();
#ifdef CONFIG_THREAD_INFO_IN_TASK
DEFINE(TSK_TI_FLAGS, offsetof(struct task_struct, thread_info.flags));
DEFINE(TSK_TI_PREEMPT, offsetof(struct task_struct, thread_info.preempt_count));
DEFINE(TSK_TI_ADDR_LIMIT, offsetof(struct task_struct, thread_info.addr_limit));
DEFINE(TSK_STACK, offsetof(struct task_struct, stack));
#else
DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
DEFINE(TI_ADDR_LIMIT, offsetof(struct thread_info, addr_limit));
#ifndef CONFIG_THREAD_INFO_IN_TASK
DEFINE(TI_TASK, offsetof(struct thread_info, task));
DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
#endif
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
DEFINE(TSK_TI_TTBR0, offsetof(struct thread_info, ttbr0));
@ -113,6 +116,11 @@ int main(void)
DEFINE(TZ_MINWEST, offsetof(struct timezone, tz_minuteswest));
DEFINE(TZ_DSTTIME, offsetof(struct timezone, tz_dsttime));
BLANK();
#ifdef CONFIG_THREAD_INFO_IN_TASK
DEFINE(CPU_BOOT_STACK, offsetof(struct secondary_data, stack));
DEFINE(CPU_BOOT_TASK, offsetof(struct secondary_data, task));
BLANK();
#endif
#ifdef CONFIG_KVM_ARM_HOST
DEFINE(VCPU_CONTEXT, offsetof(struct kvm_vcpu, arch.ctxt));
DEFINE(CPU_GP_REGS, offsetof(struct kvm_cpu_context, gp_regs));

58
arch/arm64/kernel/entry.S
View file

@ -93,9 +93,14 @@
.if \el == 0
mrs x21, sp_el0
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr_this_cpu tsk, __entry_task, x20 // Ensure MDSCR_EL1.SS is clear,
ldr x19, [tsk, #TSK_TI_FLAGS] // since we can unmask debug
#else
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
#endif
disable_step_tsk x19, x20 // exceptions when scheduling.
mov x29, xzr // fp pointed to user-space
@ -103,10 +108,18 @@
add x21, sp, #S_FRAME_SIZE
get_thread_info tsk
/* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x20, [tsk, #TSK_TI_ADDR_LIMIT]
#else
ldr x20, [tsk, #TI_ADDR_LIMIT]
#endif
str x20, [sp, #S_ORIG_ADDR_LIMIT]
mov x20, #TASK_SIZE_64
#ifdef CONFIG_THREAD_INFO_IN_TASK
str x20, [tsk, #TSK_TI_ADDR_LIMIT]
#else
str x20, [tsk, #TI_ADDR_LIMIT]
#endif
ALTERNATIVE(nop, SET_PSTATE_UAO(0), ARM64_HAS_UAO, CONFIG_ARM64_UAO)
.endif /* \el == 0 */
mrs x22, elr_el1
@ -168,7 +181,11 @@ alternative_else_nop_endif
.if \el != 0
/* Restore the task's original addr_limit. */
ldr x20, [sp, #S_ORIG_ADDR_LIMIT]
#ifdef CONFIG_THREAD_INFO_IN_TASK
str x20, [tsk, #TSK_TI_ADDR_LIMIT]
#else
str x20, [tsk, #TI_ADDR_LIMIT]
#endif
/* No need to restore UAO, it will be restored from SPSR_EL1 */
.endif
@ -258,13 +275,20 @@ alternative_endif
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.
*/
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x25, [tsk, TSK_STACK]
eor x25, x25, x19
and x25, x25, #~(THREAD_SIZE - 1)
cbnz x25, 9998f
#else
and x25, x19, #~(THREAD_SIZE - 1)
cmp x25, tsk
b.ne 9998f
#endif
adr_this_cpu x25, irq_stack, x26
mov x26, #IRQ_STACK_START_SP
@ -493,9 +517,17 @@ el1_irq:
irq_handler
#ifdef CONFIG_PREEMPT
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr w24, [tsk, #TSK_TI_PREEMPT] // get preempt count
#else
ldr w24, [tsk, #TI_PREEMPT] // get preempt count
#endif
cbnz w24, 1f // preempt count != 0
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
#else
ldr x0, [tsk, #TI_FLAGS] // get flags
#endif
tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
bl el1_preempt
1:
@ -510,7 +542,11 @@ ENDPROC(el1_irq)
el1_preempt:
mov x24, lr
1: bl preempt_schedule_irq // irq en/disable is done inside
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x0, [tsk, #TSK_TI_FLAGS] // get new tasks TI_FLAGS
#else
ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS
#endif
tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling?
ret x24
#endif
@ -730,8 +766,12 @@ ENTRY(cpu_switch_to)
ldp x29, x9, [x8], #16
ldr lr, [x8]
mov sp, x9
#ifdef CONFIG_THREAD_INFO_IN_TASK
msr sp_el0, x1
#else
and x9, x9, #~(THREAD_SIZE - 1)
msr sp_el0, x9
#endif
ret
ENDPROC(cpu_switch_to)
@ -742,7 +782,11 @@ ENDPROC(cpu_switch_to)
ret_fast_syscall:
disable_irq // disable interrupts
str x0, [sp, #S_X0] // returned x0
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
#else
ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing
#endif
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
and x2, x1, #_TIF_WORK_MASK
@ -774,7 +818,11 @@ work_resched:
*/
ret_to_user:
disable_irq // disable interrupts
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x1, [tsk, #TSK_TI_FLAGS]
#else
ldr x1, [tsk, #TI_FLAGS]
#endif
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
enable_step_tsk x1, x2
@ -806,7 +854,11 @@ el0_svc_naked: // compat entry point
enable_dbg_and_irq
ct_user_exit 1
#ifdef CONFIG_THREAD_INFO_IN_TASK
ldr x16, [tsk, #TSK_TI_FLAGS] // check for syscall hooks
#else
ldr x16, [tsk, #TI_FLAGS] // check for syscall hooks
#endif
tst x16, #_TIF_SYSCALL_WORK
b.ne __sys_trace
cmp scno, sc_nr // check upper syscall limit

18
arch/arm64/kernel/head.S
View file

@ -424,6 +424,7 @@ kernel_img_size:
.set initial_sp, init_thread_union + THREAD_START_SP
__mmap_switched:
mov x28, lr // preserve LR
adr_l x8, vectors // load VBAR_EL1 with virtual
msr vbar_el1, x8 // vector table address
isb
@ -474,10 +475,18 @@ __mmap_switched:
dsb sy // with MMU off
#endif
#ifdef CONFIG_THREAD_INFO_IN_TASK
adrp x4, init_thread_union
add sp, x4, #THREAD_SIZE
adr_l x5, init_task
msr sp_el0, x5 // Save thread_info
#else
adr_l sp, initial_sp, x4
mov x4, sp
and x4, x4, #~(THREAD_SIZE - 1)
msr sp_el0, x4 // Save thread_info
#endif
str_l x21, __fdt_pointer, x5 // Save FDT pointer
ldr_l x4, kimage_vaddr // Save the offset between
@ -689,11 +698,18 @@ ENTRY(__secondary_switched)
adr_l x5, vectors
msr vbar_el1, x5
isb
#ifdef CONFIG_THREAD_INFO_IN_TASK
adr_l x0, secondary_data
ldr x1, [x0, #CPU_BOOT_STACK] // get secondary_data.stack
mov sp, x1
ldr x2, [x0, #CPU_BOOT_TASK]
msr sp_el0, x2
#else
ldr_l x0, secondary_data // get secondary_data.stack
mov sp, x0
and x0, x0, #~(THREAD_SIZE - 1)
msr sp_el0, x0 // save thread_info
#endif
mov x29, #0
b secondary_start_kernel
ENDPROC(__secondary_switched)

22
arch/arm64/kernel/process.c
View file

@ -45,6 +45,9 @@
#include <linux/personality.h>
#include <linux/notifier.h>
#include <trace/events/power.h>
#ifdef CONFIG_THREAD_INFO_IN_TASK
#include <linux/percpu.h>
#endif
#include <asm/alternative.h>
#include <asm/compat.h>
@ -390,6 +393,22 @@ void uao_thread_switch(struct task_struct *next)
}
}
#ifdef CONFIG_THREAD_INFO_IN_TASK
/*
* We store our current task in sp_el0, which is clobbered by userspace. Keep a
* shadow copy so that we can restore this upon entry from userspace.
*
* This is *only* for exception entry from EL0, and is not valid until we
* __switch_to() a user task.
*/
DEFINE_PER_CPU(struct task_struct *, __entry_task);
static void entry_task_switch(struct task_struct *next)
{
__this_cpu_write(__entry_task, next);
}
#endif
/*
* Thread switching.
*/
@ -402,6 +421,9 @@ struct task_struct *__switch_to(struct task_struct *prev,
tls_thread_switch(next);
hw_breakpoint_thread_switch(next);
contextidr_thread_switch(next);
#ifdef CONFIG_THREAD_INFO_IN_TASK
entry_task_switch(next);
#endif
uao_thread_switch(next);
/*

6
arch/arm64/kernel/smp.c
View file

@ -98,6 +98,9 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
* We need to tell the secondary core where to find its stack and the
* page tables.
*/
#ifdef CONFIG_THREAD_INFO_IN_TASK
secondary_data.task = idle;
#endif
secondary_data.stack = task_stack_page(idle) + THREAD_START_SP;
__flush_dcache_area(&secondary_data, sizeof(secondary_data));
@ -121,6 +124,9 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
}
#ifdef CONFIG_THREAD_INFO_IN_TASK
secondary_data.task = NULL;
#endif
secondary_data.stack = NULL;
return ret;