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    SubjectRe: [PATCH 2/2] x86/boot: increase maximum number of avoided KASLR regions
    On Wed, Jan 30, 2019 at 05:40:03PM +0100, Julian Stecklina wrote:
    > From: Julian Stecklina <jsteckli@amazon.de>
    >
    > The boot code has a limit of 4 "non-standard" regions to avoid for
    > KASLR. This limit is easy to reach when supplying memmap= parameters to
    > the kernel. In this case, KASLR would be disabled.
    >
    > Increase the limit to avoid turning off KASLR even when the user is
    > heavily manipulating the memory map.
    >
    > Signed-off-by: Julian Stecklina <jsteckli@amazon.de>
    > ---
    > arch/x86/boot/compressed/kaslr.c | 6 +++---
    > 1 file changed, 3 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
    > index 5657e34..f078d60 100644
    > --- a/arch/x86/boot/compressed/kaslr.c
    > +++ b/arch/x86/boot/compressed/kaslr.c
    > @@ -92,8 +92,8 @@ struct mem_vector {
    > unsigned long long size;
    > };
    >
    > -/* Only supporting at most 4 unusable memmap regions with kaslr */
    > -#define MAX_MEMMAP_REGIONS 4
    > +/* Only supporting at most this many unusable memmap regions with kaslr */
    > +#define MAX_MEMMAP_REGIONS 16
    >
    > static bool memmap_too_large;
    >
    > @@ -213,7 +213,7 @@ static void mem_avoid_memmap(char *str)
    > i++;
    > }
    >
    > - /* More than 4 memmaps, fail kaslr */
    > + /* Can't store all regions, fail kaslr */
    > if ((i >= MAX_MEMMAP_REGIONS) && str)
    > memmap_too_large = true;
    > }
    > --

    Lemme add some of the folks from
    f28442497b5caf7bf573ade22a7f8d3559e3ef56 to Cc.

    It all looks arbitrary to me: first 4 unusable memmap regions, this
    patch raises it to 16. Why are we even imposing such a limit?

    Hmm.

    --
    Regards/Gruss,
    Boris.

    Good mailing practices for 400: avoid top-posting and trim the reply.

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