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    Subject[PATCH v3 06/12] parisc: Use initializer for struct vm_unmapped_area_info
    Date
    Future changes will need to add a new member to struct
    vm_unmapped_area_info. This would cause trouble for any call site that
    doesn't initialize the struct. Currently every caller sets each member
    manually, so if new members are added they will be uninitialized and the
    core code parsing the struct will see garbage in the new member.

    It could be possible to initialize the new member manually to 0 at each
    call site. This and a couple other options were discussed, and a working
    consensus (see links) was that in general the best way to accomplish this
    would be via static initialization with designated member initiators.
    Having some struct vm_unmapped_area_info instances not zero initialized
    will put those sites at risk of feeding garbage into vm_unmapped_area() if
    the convention is to zero initialize the struct and any new member addition
    misses a call site that initializes each member manually.

    It could be possible to leave the code mostly untouched, and just change
    the line:
    struct vm_unmapped_area_info info
    to:
    struct vm_unmapped_area_info info = {};

    However, that would leave cleanup for the members that are manually set
    to zero, as it would no longer be required.

    So to be reduce the chance of bugs via uninitialized members, instead
    simply continue the process to initialize the struct this way tree wide.
    This will zero any unspecified members. Move the member initializers to the
    struct declaration when they are known at that time. Leave the members out
    that were manually initialized to zero, as this would be redundant for
    designated initializers.

    Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    Acked-by: Helge Deller <deller@gmx.de>
    Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
    Cc: Helge Deller <deller@gmx.de>
    Cc: linux-parisc@vger.kernel.org
    Link: https://lore.kernel.org/lkml/202402280912.33AEE7A9CF@keescook/#t
    Link: https://lore.kernel.org/lkml/j7bfvig3gew3qruouxrh7z7ehjjafrgkbcmg6tcghhfh3rhmzi@wzlcoecgy5rs/
    ---
    v3:
    - Fixed spelling errors in log
    - Be consistent about field vs member in log

    Hi,

    This patch was split and refactored out of a tree-wide change [0] to just
    zero-init each struct vm_unmapped_area_info. The overall goal of the
    series is to help shadow stack guard gaps. Currently, there is only one
    arch with shadow stacks, but two more are in progress. It is compile tested
    only.

    There was further discussion that this method of initializing the structs
    while nice in some ways has a greater risk of introducing bugs in some of
    the more complicated callers. Since this version was reviewed my arch
    maintainers already, leave it as was already acknowledged.

    Thanks,

    Rick

    [0] https://lore.kernel.org/lkml/20240226190951.3240433-6-rick.p.edgecombe@intel.com/
    ---
    arch/parisc/kernel/sys_parisc.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
    index 98af719d5f85..f7722451276e 100644
    --- a/arch/parisc/kernel/sys_parisc.c
    +++ b/arch/parisc/kernel/sys_parisc.c
    @@ -104,7 +104,9 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
    struct vm_area_struct *vma, *prev;
    unsigned long filp_pgoff;
    int do_color_align;
    - struct vm_unmapped_area_info info;
    + struct vm_unmapped_area_info info = {
    + .length = len
    + };

    if (unlikely(len > TASK_SIZE))
    return -ENOMEM;
    @@ -139,7 +141,6 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
    return addr;
    }

    - info.length = len;
    info.align_mask = do_color_align ? (PAGE_MASK & (SHM_COLOUR - 1)) : 0;
    info.align_offset = shared_align_offset(filp_pgoff, pgoff);

    @@ -160,7 +161,6 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
    */
    }

    - info.flags = 0;
    info.low_limit = mm->mmap_base;
    info.high_limit = mmap_upper_limit(NULL);
    return vm_unmapped_area(&info);
    --
    2.34.1

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