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    Subject[PATCH 5.19 0767/1157] kasan: fix zeroing vmalloc memory with HW_TAGS
    Date
    From: Andrey Konovalov <andreyknvl@google.com>

    [ Upstream commit 6c2f761dad7851d8088b91063ccaea3c970efe78 ]

    HW_TAGS KASAN skips zeroing page_alloc allocations backing vmalloc
    mappings via __GFP_SKIP_ZERO. Instead, these pages are zeroed via
    kasan_unpoison_vmalloc() by passing the KASAN_VMALLOC_INIT flag.

    The problem is that __kasan_unpoison_vmalloc() does not zero pages when
    either kasan_vmalloc_enabled() or is_vmalloc_or_module_addr() fail.

    Thus:

    1. Change __vmalloc_node_range() to only set KASAN_VMALLOC_INIT when
    __GFP_SKIP_ZERO is set.

    2. Change __kasan_unpoison_vmalloc() to always zero pages when the
    KASAN_VMALLOC_INIT flag is set.

    3. Add WARN_ON() asserts to check that KASAN_VMALLOC_INIT cannot be set
    in other early return paths of __kasan_unpoison_vmalloc().

    Also clean up the comment in __kasan_unpoison_vmalloc.

    Link: https://lkml.kernel.org/r/4bc503537efdc539ffc3f461c1b70162eea31cf6.1654798516.git.andreyknvl@google.com
    Fixes: 23689e91fb22 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS")
    Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
    Cc: Marco Elver <elver@google.com>
    Cc: Alexander Potapenko <glider@google.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/kasan/hw_tags.c | 32 +++++++++++++++++++++++---------
    mm/vmalloc.c | 10 +++++-----
    2 files changed, 28 insertions(+), 14 deletions(-)

    diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
    index 9e1b6544bfa8..9ad8eff71b28 100644
    --- a/mm/kasan/hw_tags.c
    +++ b/mm/kasan/hw_tags.c
    @@ -257,27 +257,37 @@ static void unpoison_vmalloc_pages(const void *addr, u8 tag)
    }
    }

    +static void init_vmalloc_pages(const void *start, unsigned long size)
    +{
    + const void *addr;
    +
    + for (addr = start; addr < start + size; addr += PAGE_SIZE) {
    + struct page *page = virt_to_page(addr);
    +
    + clear_highpage_kasan_tagged(page);
    + }
    +}
    +
    void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
    kasan_vmalloc_flags_t flags)
    {
    u8 tag;
    unsigned long redzone_start, redzone_size;

    - if (!kasan_vmalloc_enabled())
    - return (void *)start;
    -
    - if (!is_vmalloc_or_module_addr(start))
    + if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
    + if (flags & KASAN_VMALLOC_INIT)
    + init_vmalloc_pages(start, size);
    return (void *)start;
    + }

    /*
    - * Skip unpoisoning and assigning a pointer tag for non-VM_ALLOC
    - * mappings as:
    + * Don't tag non-VM_ALLOC mappings, as:
    *
    * 1. Unlike the software KASAN modes, hardware tag-based KASAN only
    * supports tagging physical memory. Therefore, it can only tag a
    * single mapping of normal physical pages.
    * 2. Hardware tag-based KASAN can only tag memory mapped with special
    - * mapping protection bits, see arch_vmalloc_pgprot_modify().
    + * mapping protection bits, see arch_vmap_pgprot_tagged().
    * As non-VM_ALLOC mappings can be mapped outside of vmalloc code,
    * providing these bits would require tracking all non-VM_ALLOC
    * mappers.
    @@ -289,15 +299,19 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
    *
    * For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
    */
    - if (!(flags & KASAN_VMALLOC_VM_ALLOC))
    + if (!(flags & KASAN_VMALLOC_VM_ALLOC)) {
    + WARN_ON(flags & KASAN_VMALLOC_INIT);
    return (void *)start;
    + }

    /*
    * Don't tag executable memory.
    * The kernel doesn't tolerate having the PC register tagged.
    */
    - if (!(flags & KASAN_VMALLOC_PROT_NORMAL))
    + if (!(flags & KASAN_VMALLOC_PROT_NORMAL)) {
    + WARN_ON(flags & KASAN_VMALLOC_INIT);
    return (void *)start;
    + }

    tag = kasan_random_tag();
    start = set_tag(start, tag);
    diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    index effd1ff6a4b4..a1ab9b472571 100644
    --- a/mm/vmalloc.c
    +++ b/mm/vmalloc.c
    @@ -3168,15 +3168,15 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,

    /*
    * Mark the pages as accessible, now that they are mapped.
    - * The init condition should match the one in post_alloc_hook()
    - * (except for the should_skip_init() check) to make sure that memory
    - * is initialized under the same conditions regardless of the enabled
    - * KASAN mode.
    + * The condition for setting KASAN_VMALLOC_INIT should complement the
    + * one in post_alloc_hook() with regards to the __GFP_SKIP_ZERO check
    + * to make sure that memory is initialized under the same conditions.
    * Tag-based KASAN modes only assign tags to normal non-executable
    * allocations, see __kasan_unpoison_vmalloc().
    */
    kasan_flags |= KASAN_VMALLOC_VM_ALLOC;
    - if (!want_init_on_free() && want_init_on_alloc(gfp_mask))
    + if (!want_init_on_free() && want_init_on_alloc(gfp_mask) &&
    + (gfp_mask & __GFP_SKIP_ZERO))
    kasan_flags |= KASAN_VMALLOC_INIT;
    /* KASAN_VMALLOC_PROT_NORMAL already set if required. */
    area->addr = kasan_unpoison_vmalloc(area->addr, real_size, kasan_flags);
    --
    2.35.1


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