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| author | Dave Hansen <dave.hansen@linux.intel.com> | 2021-06-23 14:02:18 +0200 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2021-06-23 19:37:45 +0200 |
| commit | 9782a712eb971ce483442076e79eb1d8d608646e (patch) | |
| tree | 841325bcb9a7248ad967ca4d1bd8bb4ca16e200f /arch/x86/kernel/process.c | |
| parent | x86/fpu: Dont restore PKRU in fpregs_restore_userspace() (diff) | |
| download | linux-9782a712eb971ce483442076e79eb1d8d608646e.tar.xz linux-9782a712eb971ce483442076e79eb1d8d608646e.zip | |
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 <dave.hansen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.399107624@linutronix.de
Diffstat (limited to 'arch/x86/kernel/process.c')
| -rw-r--r-- | arch/x86/kernel/process.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index de942b038815..fa6c8fa0f778 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -156,11 +156,18 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg, /* Kernel thread ? */ if (unlikely(p->flags & PF_KTHREAD)) { + p->thread.pkru = pkru_get_init_value(); memset(childregs, 0, sizeof(struct pt_regs)); kthread_frame_init(frame, sp, arg); return 0; } + /* + * Clone current's PKRU value from hardware. tsk->thread.pkru + * is only valid when scheduled out. + */ + p->thread.pkru = read_pkru(); + frame->bx = 0; *childregs = *current_pt_regs(); childregs->ax = 0; |