lkml.org 
[lkml]   [2017]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Subject[PATCH 12/30] x86, kaiser: map GDT into user page tables
    From
    Date

    From: Dave Hansen <dave.hansen@linux.intel.com>

    The GDT is used to control the x86 segmentation mechanism. It
    must be virtually mapped when switching segments or at IRET
    time when switching between userspace and kernel.

    The original KAISER patch did not do this. I have no ide how
    it ever worked.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
    Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
    Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
    Cc: Richard Fellner <richard.fellner@student.tugraz.at>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Kees Cook <keescook@google.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: x86@kernel.org
    ---

    b/arch/x86/kernel/cpu/common.c | 15 +++++++++++++++
    b/arch/x86/mm/kaiser.c | 10 ++++++++++
    2 files changed, 25 insertions(+)

    diff -puN arch/x86/kernel/cpu/common.c~kaiser-user-map-gdt-pages arch/x86/kernel/cpu/common.c
    --- a/arch/x86/kernel/cpu/common.c~kaiser-user-map-gdt-pages 2017-11-08 10:45:32.375681387 -0800
    +++ b/arch/x86/kernel/cpu/common.c 2017-11-08 10:45:32.380681387 -0800
    @@ -5,6 +5,7 @@
    #include <linux/export.h>
    #include <linux/percpu.h>
    #include <linux/string.h>
    +#include <linux/kaiser.h>
    #include <linux/ctype.h>
    #include <linux/delay.h>
    #include <linux/sched/mm.h>
    @@ -487,6 +488,20 @@ static inline void setup_fixmap_gdt(int
    #endif

    __set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
    +
    + /* CPU 0's mapping is done in kaiser_init() */
    + if (cpu) {
    + int ret;
    +
    + ret = kaiser_add_mapping((unsigned long) get_cpu_gdt_ro(cpu),
    + PAGE_SIZE, __PAGE_KERNEL_RO);
    + /*
    + * We do not have a good way to fail CPU bringup.
    + * Just WARN about it and hope we boot far enough
    + * to get a good log out.
    + */
    + WARN_ON(ret);
    + }
    }

    /* Load the original GDT from the per-cpu structure */
    diff -puN arch/x86/mm/kaiser.c~kaiser-user-map-gdt-pages arch/x86/mm/kaiser.c
    --- a/arch/x86/mm/kaiser.c~kaiser-user-map-gdt-pages 2017-11-08 10:45:32.376681387 -0800
    +++ b/arch/x86/mm/kaiser.c 2017-11-08 10:45:32.380681387 -0800
    @@ -361,6 +361,16 @@ void __init kaiser_init(void)
    kaiser_add_user_map_early((void *)idt_descr.address,
    sizeof(gate_desc) * NR_VECTORS,
    __PAGE_KERNEL_RO | _PAGE_GLOBAL);
    +
    + /*
    + * We could theoretically do this in setup_fixmap_gdt().
    + * But, we would need to rewrite the above page table
    + * allocation code to use the bootmem allocator. The
    + * buddy allocator is not available at the time that we
    + * call setup_fixmap_gdt() for CPU 0.
    + */
    + kaiser_add_user_map_early(get_cpu_gdt_ro(0), PAGE_SIZE,
    + __PAGE_KERNEL_RO | _PAGE_GLOBAL);
    }

    int kaiser_add_mapping(unsigned long addr, unsigned long size,
    _
    \
     
     \ /
      Last update: 2017-11-08 21:15    [W:6.479 / U:0.104 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site