| Date | Tue, 22 Jun 2021 18:55:01 +0200 | From | Borislav Petkov <> | Subject | Re: [patch V3 52/66] x86/fpu: Add PKRU storage outside of task XSAVE buffer |
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On Fri, Jun 18, 2021 at 04:19:15PM +0200, Thomas Gleixner wrote: > From: Dave Hansen <dave.hansen@linux.intel.com> > > PKRU is currently partly XSAVE-managed and partly not. It has space in the > task XSAVE buffer and is context-switched by XSAVE/XRSTOR. However, it is > switched more eagerly than FPU because there may be a need for PKRU to be > up-to-date for things like copy_to/from_user() since PKRU affects > user-permission memory accesses, not just accesses from userspace itself. > > This leaves PKRU in a very odd position. XSAVE brings very little value to > the table for how Linux uses PKRU except for signal related XSTATE > handling. > > Prepare to move PKRU away from being XSAVE-managed. Allocate space in the > thread_struct for it and save/restore it in the context-switch path > separately from the XSAVE-managed features. task->thread_struct.pkru is > only valid when the task is scheduled out. For the current task the > authoritative source is the hardware, i.e. it has to be retrieved via > rdpkru(). > > Leave the XSAVE code in place for now to ensure bisectability. > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > V3: Fix the fallout on !PKRU enabled systems in copy_thread() - Intel testing via Dave > --- > arch/x86/include/asm/processor.h | 9 +++++++++ > arch/x86/kernel/process.c | 7 +++++++ > arch/x86/kernel/process_64.c | 25 +++++++++++++++++++++++++ > 3 files changed, 41 insertions(+)
Reviewed-by: Borislav Petkov <bp@suse.de>
-- Regards/Gruss, Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
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