From 9782a712eb971ce483442076e79eb1d8d608646e Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Wed, 23 Jun 2021 14:02:18 +0200 Subject: x86/fpu: Add PKRU storage outside of task XSAVE buffer 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 Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov Reviewed-by: Borislav Petkov Link: https://lkml.kernel.org/r/20210623121456.399107624@linutronix.de --- arch/x86/include/asm/processor.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/x86/include/asm/processor.h') diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 556b2b17c3e2..91946fc3c006 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -518,6 +518,15 @@ struct thread_struct { unsigned int sig_on_uaccess_err:1; + /* + * Protection Keys Register for Userspace. Loaded immediately on + * context switch. Store it in thread_struct to avoid a lookup in + * the tasks's FPU xstate buffer. This value is only valid when a + * task is scheduled out. For 'current' the authoritative source of + * PKRU is the hardware itself. + */ + u32 pkru; + /* Floating point and extended processor state */ struct fpu fpu; /* -- cgit