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  • Joerg Roedel's avatar
    x86, vmlinux.lds: Page-align end of ..page_aligned sections · de2b41be
    Joerg Roedel authored
    
    
    On x86-32 the idt_table with 256 entries needs only 2048 bytes. It is
    page-aligned, but the end of the .bss..page_aligned section is not
    guaranteed to be page-aligned.
    
    As a result, objects from other .bss sections may end up on the same 4k
    page as the idt_table, and will accidentially get mapped read-only during
    boot, causing unexpected page-faults when the kernel writes to them.
    
    This could be worked around by making the objects in the page aligned
    sections page sized, but that's wrong.
    
    Explicit sections which store only page aligned objects have an implicit
    guarantee that the object is alone in the page in which it is placed. That
    works for all objects except the last one. That's inconsistent.
    
    Enforcing page sized objects for these sections would wreckage memory
    sanitizers, because the object becomes artificially larger than it should
    be and out of bound access becomes legit.
    
    Align the end of the .bss..page_aligned and .data..page_aligned section on
    page-size so all objects places in these sections are guaranteed to have
    their own page.
    
    [ tglx: Amended changelog ]
    
    Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: default avatarKees Cook <keescook@chromium.org>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20200721093448.10417-1-joro@8bytes.org
    de2b41be