Messages in this thread | | | Date | Fri, 8 Jan 2016 20:40:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 29/31] x86, pkeys: allow kernel to modify user pkey rights register |
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On Wed, 6 Jan 2016, Dave Hansen wrote: > From: Dave Hansen <dave.hansen@linux.intel.com> > > The Protection Key Rights for User memory (PKRU) is a 32-bit > user-accessible register. It contains two bits for each > protection key: one to write-disable (WD) access to memory > covered by the key and another to access-disable (AD). > > Userspace can read/write the register with the RDPKRU and WRPKRU > instructions. But, the register is saved and restored with the > XSAVE family of instructions, which means we have to treat it > like a floating point register. > > The kernel needs to write to the register if it wants to > implement execute-only memory or if it implements a system call > to change PKRU. > > To do this, we need to create a 'pkru_state' buffer, read the old > contents in to it, modify it, and then tell the FPU code that > there is modified data in there so it can (possibly) move the > buffer back in to the registers. > > This uses the fpu__xfeature_set_state() function that we defined > in the previous patch. > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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