| From | Andy Lutomirski <> | Date | Mon, 4 Dec 2017 14:28:46 -0800 | Subject | Re: [patch 35/60] x86/espfix: Ensure that ESPFIX is visible in user PGD |
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On Mon, Dec 4, 2017 at 6:07 AM, Thomas Gleixner <tglx@linutronix.de> wrote: > From: Dave Hansen <dave.hansen@linux.intel.com> > > Clone the ESPFIX alias mapping area so the entry/exit code has access to it > even with the user space page tables. > > [ tglx: Remove the per cpu user mapped oddity ] > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > --- > arch/x86/kernel/espfix_64.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > --- a/arch/x86/kernel/espfix_64.c > +++ b/arch/x86/kernel/espfix_64.c > @@ -129,6 +129,22 @@ void __init init_espfix_bsp(void) > p4d = p4d_alloc(&init_mm, pgd, ESPFIX_BASE_ADDR); > p4d_populate(&init_mm, p4d, espfix_pud_page); > > + /* > + * Just copy the top-level PGD that is mapping the espfix area to > + * ensure it is mapped into the user page tables. > + * > + * For 5-level paging, the espfix pgd was populated when > + * kpti_init() pre-populated all the pgd entries. The above > + * p4d_alloc() would never do anything and the p4d_populate() would > + * be done to a p4d already mapped in the userspace pgd. > + */
Is this actually true? From brief inspection, it doesn't seem to be the case, nor do I see why it should be true.
> +#ifdef CONFIG_KERNEL_PAGE_TABLE_ISOLATION > + if (CONFIG_PGTABLE_LEVELS <= 4) { > + set_pgd(kernel_to_user_pgdp(pgd), > + __pgd(_KERNPG_TABLE | (p4d_pfn(*p4d) << PAGE_SHIFT))); > + } > +#endif > + > /* Randomize the locations */ > init_espfix_random(); > > >
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