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| author | Dave Martin <Dave.Martin@arm.com> | 2017-12-06 19:45:47 +0300 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2017-12-06 22:08:05 +0300 |
| commit | cb968afc789821cdf9e17e79ef08ab90e5bae0f2 (patch) | |
| tree | bfebdce5e2dd33cc1c05aa9dbd574bd8cc933b6b /arch | |
| parent | d96cc49bff5a7735576cc6f6f111f875d101cec8 (diff) | |
| download | linux-cb968afc789821cdf9e17e79ef08ab90e5bae0f2.tar.xz | |
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')
| -rw-r--r-- | arch/arm64/kernel/fpsimd.c | 28 |
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 = ¤t->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; } |