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authorDave Martin <Dave.Martin@arm.com>2017-12-06 16:45:47 +0000
committerWill Deacon <will.deacon@arm.com>2017-12-06 19:08:05 +0000
commitcb968afc789821cdf9e17e79ef08ab90e5bae0f2 (patch)
treebfebdce5e2dd33cc1c05aa9dbd574bd8cc933b6b /arch/arm64/kernel/fpsimd.c
parentd96cc49bff5a7735576cc6f6f111f875d101cec8 (diff)
arm64/sve: Avoid dereference of dead task_struct in KVM guest entry
When deciding whether to invalidate FPSIMD state cached in the cpu, the backend function sve_flush_cpu_state() attempts to dereference __this_cpu_read(fpsimd_last_state). However, this is not safe: there is no guarantee that this task_struct pointer is still valid, because the task could have exited in the meantime. This means that we need another means to get the appropriate value of TIF_SVE for the associated task. This patch solves this issue by adding a cached copy of the TIF_SVE flag in fpsimd_last_state, which we can check without dereferencing the task pointer. In particular, although this patch is not a KVM fix per se, this means that this check is now done safely in the KVM world switch path (which is currently the only user of this code). Signed-off-by: Dave Martin <Dave.Martin@arm.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/kernel/fpsimd.c')
-rw-r--r--arch/arm64/kernel/fpsimd.c28
1 files changed, 16 insertions, 12 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e330cc0b573d..540a1e010eb5 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -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
@@ -997,9 +1002,12 @@ void fpsimd_signal_preserve_current_state(void)
*/
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;
- __this_cpu_write(fpsimd_last_state, st);
+ last->st = st;
+ last->sve_in_use = test_thread_flag(TIF_SVE);
st->cpu = smp_processor_id();
}
@@ -1057,7 +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);
}
/*
@@ -1070,14 +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;
-
- if (!fpstate)
- return;
+ struct fpsimd_last_state_struct const *last =
+ this_cpu_ptr(&fpsimd_last_state);
- 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 */
@@ -1272,7 +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;
}