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    Subject[PATCH 5.4 351/475] powerpc/kasan: Fix early region not updated correctly
    Date
    From: Chen Jingwen <chenjingwen6@huawei.com>

    commit dd75080aa8409ce10d50fb58981c6b59bf8707d3 upstream.

    The shadow's page table is not updated when PTE_RPN_SHIFT is 24
    and PAGE_SHIFT is 12. It not only causes false positives but
    also false negative as shown the following text.

    Fix it by bringing the logic of kasan_early_shadow_page_entry here.

    1. False Positive:
    ==================================================================
    BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50
    Write of size 16 at addr f57f3be0 by task swapper/0/1

    CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.15.0-12267-gdebe436e77c7 #1
    Call Trace:
    [c80d1c20] [c07fe7b8] dump_stack_lvl+0x4c/0x6c (unreliable)
    [c80d1c40] [c02ff668] print_address_description.constprop.0+0x88/0x300
    [c80d1c70] [c02ff45c] kasan_report+0x1ec/0x200
    [c80d1cb0] [c0300b20] kasan_check_range+0x160/0x2f0
    [c80d1cc0] [c03018a4] memset+0x34/0x90
    [c80d1ce0] [c0280108] pcpu_alloc+0x508/0xa50
    [c80d1d40] [c02fd7bc] __kmem_cache_create+0xfc/0x570
    [c80d1d70] [c0283d64] kmem_cache_create_usercopy+0x274/0x3e0
    [c80d1db0] [c2036580] init_sd+0xc4/0x1d0
    [c80d1de0] [c00044a0] do_one_initcall+0xc0/0x33c
    [c80d1eb0] [c2001624] kernel_init_freeable+0x2c8/0x384
    [c80d1ef0] [c0004b14] kernel_init+0x24/0x170
    [c80d1f10] [c001b26c] ret_from_kernel_thread+0x5c/0x64

    Memory state around the buggy address:
    f57f3a80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    f57f3b00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    >f57f3b80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ^
    f57f3c00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    f57f3c80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ==================================================================

    2. False Negative (with KASAN tests):
    ==================================================================
    Before fix:
    ok 45 - kmalloc_double_kzfree
    # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:1039
    KASAN failure expected in "((volatile char *)area)[3100]", but none occurred
    not ok 46 - vmalloc_oob
    not ok 1 - kasan

    ==================================================================
    After fix:
    ok 1 - kasan

    Fixes: cbd18991e24fe ("powerpc/mm: Fix an Oops in kasan_mmu_init()")
    Cc: stable@vger.kernel.org # 5.4.x
    Signed-off-by: Chen Jingwen <chenjingwen6@huawei.com>
    Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20211229035226.59159-1-chenjingwen6@huawei.com
    [chleroy: Backport for 5.4]
    Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/mm/kasan/kasan_init_32.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/powerpc/mm/kasan/kasan_init_32.c
    +++ b/arch/powerpc/mm/kasan/kasan_init_32.c
    @@ -121,7 +121,7 @@ static void __init kasan_remap_early_sha
    pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(k_cur), k_cur), k_cur);
    pte_t *ptep = pte_offset_kernel(pmd, k_cur);

    - if ((pte_val(*ptep) & PTE_RPN_MASK) != pa)
    + if (pte_page(*ptep) != virt_to_page(lm_alias(kasan_early_shadow_page)))
    continue;

    __set_pte_at(&init_mm, k_cur, ptep, pfn_pte(PHYS_PFN(pa), prot), 0);

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