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arm64 fixes: 

- Fix SW PAN pgd shadowing for kernel threads, EFI and exiting user tasks
 
 - Fix FP register leak when a task_struct is re-allocated
 
 - Fix potential use-after-free in FP state tracking used by KVM
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Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fixes from Will Deacon:
 "Fix some more FP register fallout from the SVE patches and also some
  problems with the PGD tracking in our software PAN emulation code,
  after we received a crash report from a 3.18 kernel running a
  backport.

  Summary:

   - fix SW PAN pgd shadowing for kernel threads, EFI and exiting user
     tasks

   - fix FP register leak when a task_struct is re-allocated

   - fix potential use-after-free in FP state tracking used by KVM"

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64/sve: Avoid dereference of dead task_struct in KVM guest entry
  arm64: SW PAN: Update saved ttbr0 value on enter_lazy_tlb
  arm64: SW PAN: Point saved ttbr0 at the zero page when switching to init_mm
  arm64: fpsimd: Abstract out binding of task's fpsimd context to the cpu.
  arm64: fpsimd: Prevent registers leaking from dead tasks
This commit is contained in:
Linus Torvalds 2017-12-08 10:08:23 -08:00
parent 3625de4b28 cb968afc78
commit 6e7e7f4ddc
4 changed files with 63 additions and 47 deletions
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4
arch/arm64/include/asm/efi.h
View File

@ -132,11 +132,9 @@ static inline void efi_set_pgd(struct mm_struct *mm)
* Defer the switch to the current thread's TTBR0_EL1
* until uaccess_enable(). Restore the current
* thread's saved ttbr0 corresponding to its active_mm
* (if different from init_mm).
*/
cpu_set_reserved_ttbr0();
if (current->active_mm != &init_mm)
update_saved_ttbr0(current, current->active_mm);
update_saved_ttbr0(current, current->active_mm);
}
}
}

46
arch/arm64/include/asm/mmu_context.h
View File

@ -156,29 +156,21 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu);
#define init_new_context(tsk,mm) ({ atomic64_set(&(mm)->context.id, 0); 0; })
/*
* This is called when "tsk" is about to enter lazy TLB mode.
*
* mm: describes the currently active mm context
* tsk: task which is entering lazy tlb
* cpu: cpu number which is entering lazy tlb
*
* tsk->mm will be NULL
*/
static inline void
enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
}
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
static inline void update_saved_ttbr0(struct task_struct *tsk,
struct mm_struct *mm)
{
if (system_uses_ttbr0_pan()) {
BUG_ON(mm->pgd == swapper_pg_dir);
task_thread_info(tsk)->ttbr0 =
virt_to_phys(mm->pgd) | ASID(mm) << 48;
}
u64 ttbr;
if (!system_uses_ttbr0_pan())
return;
if (mm == &init_mm)
ttbr = __pa_symbol(empty_zero_page);
else
ttbr = virt_to_phys(mm->pgd) | ASID(mm) << 48;
task_thread_info(tsk)->ttbr0 = ttbr;
}
#else
static inline void update_saved_ttbr0(struct task_struct *tsk,
@ -187,6 +179,16 @@ static inline void update_saved_ttbr0(struct task_struct *tsk,
}
#endif
static inline void
enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
/*
* We don't actually care about the ttbr0 mapping, so point it at the
* zero page.
*/
update_saved_ttbr0(tsk, &init_mm);
}
static inline void __switch_mm(struct mm_struct *next)
{
unsigned int cpu = smp_processor_id();
@ -214,11 +216,9 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
* Update the saved TTBR0_EL1 of the scheduled-in task as the previous
* value may have not been initialised yet (activate_mm caller) or the
* ASID has changed since the last run (following the context switch
* of another thread of the same process). Avoid setting the reserved
* TTBR0_EL1 to swapper_pg_dir (init_mm; e.g. via idle_task_exit).
* of another thread of the same process).
*/
if (next != &init_mm)
update_saved_ttbr0(tsk, next);
update_saved_ttbr0(tsk, next);
}
#define deactivate_mm(tsk,mm) do { } while (0)

51
arch/arm64/kernel/fpsimd.c
View File

@ -114,7 +114,12 @@
* returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
* whatever is in the FPSIMD registers is not saved to memory, but discarded.
*/
static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
struct fpsimd_last_state_struct {
struct fpsimd_state *st;
bool sve_in_use;
};
static DEFINE_PER_CPU(struct fpsimd_last_state_struct, fpsimd_last_state);
/* Default VL for tasks that don't set it explicitly: */
static int sve_default_vl = -1;
@ -905,7 +910,7 @@ void fpsimd_thread_switch(struct task_struct *next)
*/
struct fpsimd_state *st = &next->thread.fpsimd_state;
if (__this_cpu_read(fpsimd_last_state) == st
if (__this_cpu_read(fpsimd_last_state.st) == st
&& st->cpu == smp_processor_id())
clear_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
else
@ -991,6 +996,21 @@ void fpsimd_signal_preserve_current_state(void)
sve_to_fpsimd(current);
}
/*
* Associate current's FPSIMD context with this cpu
* Preemption must be disabled when calling this function.
*/
static void fpsimd_bind_to_cpu(void)
{
struct fpsimd_last_state_struct *last =
this_cpu_ptr(&fpsimd_last_state);
struct fpsimd_state *st = &current->thread.fpsimd_state;
last->st = st;
last->sve_in_use = test_thread_flag(TIF_SVE);
st->cpu = smp_processor_id();
}
/*
* Load the userland FPSIMD state of 'current' from memory, but only if the
* FPSIMD state already held in the registers is /not/ the most recent FPSIMD
@ -1004,11 +1024,8 @@ void fpsimd_restore_current_state(void)
local_bh_disable();
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
struct fpsimd_state *st = &current->thread.fpsimd_state;
task_fpsimd_load();
__this_cpu_write(fpsimd_last_state, st);
st->cpu = smp_processor_id();
fpsimd_bind_to_cpu();
}
local_bh_enable();
@ -1032,12 +1049,8 @@ void fpsimd_update_current_state(struct fpsimd_state *state)
task_fpsimd_load();
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
struct fpsimd_state *st = &current->thread.fpsimd_state;
__this_cpu_write(fpsimd_last_state, st);
st->cpu = smp_processor_id();
}
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE))
fpsimd_bind_to_cpu();
local_bh_enable();
}
@ -1052,7 +1065,7 @@ void fpsimd_flush_task_state(struct task_struct *t)
static inline void fpsimd_flush_cpu_state(void)
{
__this_cpu_write(fpsimd_last_state, NULL);
__this_cpu_write(fpsimd_last_state.st, NULL);
}
/*
@ -1065,14 +1078,10 @@ static inline void fpsimd_flush_cpu_state(void)
#ifdef CONFIG_ARM64_SVE
void sve_flush_cpu_state(void)
{
struct fpsimd_state *const fpstate = __this_cpu_read(fpsimd_last_state);
struct task_struct *tsk;
struct fpsimd_last_state_struct const *last =
this_cpu_ptr(&fpsimd_last_state);
if (!fpstate)
return;
tsk = container_of(fpstate, struct task_struct, thread.fpsimd_state);
if (test_tsk_thread_flag(tsk, TIF_SVE))
if (last->st && last->sve_in_use)
fpsimd_flush_cpu_state();
}
#endif /* CONFIG_ARM64_SVE */
@ -1267,7 +1276,7 @@ static inline void fpsimd_pm_init(void) { }
#ifdef CONFIG_HOTPLUG_CPU
static int fpsimd_cpu_dead(unsigned int cpu)
{
per_cpu(fpsimd_last_state, cpu) = NULL;
per_cpu(fpsimd_last_state.st, cpu) = NULL;
return 0;
}

9
arch/arm64/kernel/process.c
View File

@ -314,6 +314,15 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
clear_tsk_thread_flag(p, TIF_SVE);
p->thread.sve_state = NULL;
/*
* In case p was allocated the same task_struct pointer as some
* other recently-exited task, make sure p is disassociated from
* any cpu that may have run that now-exited task recently.
* Otherwise we could erroneously skip reloading the FPSIMD
* registers for p.
*/
fpsimd_flush_task_state(p);
if (likely(!(p->flags & PF_KTHREAD))) {
*childregs = *current_pt_regs();
childregs->regs[0] = 0;