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    Subject[PATCH 5.14 396/849] scs: Release kasan vmalloc poison in scs_free process
    Date
    From: Yee Lee <yee.lee@mediatek.com>

    [ Upstream commit 528a4ab45300fa6283556d9b48e26b45a8aa15c4 ]

    Since scs allocation is moved to vmalloc region, the
    shadow stack is protected by kasan_posion_vmalloc.
    However, the vfree_atomic operation needs to access
    its context for scs_free process and causes kasan error
    as the dump info below.

    This patch Adds kasan_unpoison_vmalloc() before vfree_atomic,
    which aligns to the prior flow as using kmem_cache.
    The vmalloc region will go back posioned in the following
    vumap() operations.

    ==================================================================
    BUG: KASAN: vmalloc-out-of-bounds in llist_add_batch+0x60/0xd4
    Write of size 8 at addr ffff8000100b9000 by task kthreadd/2

    CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.15.0-rc2-11681-g92477dd1faa6-dirty #1
    Hardware name: linux,dummy-virt (DT)
    Call trace:
    dump_backtrace+0x0/0x43c
    show_stack+0x1c/0x2c
    dump_stack_lvl+0x68/0x84
    print_address_description+0x80/0x394
    kasan_report+0x180/0x1dc
    __asan_report_store8_noabort+0x48/0x58
    llist_add_batch+0x60/0xd4
    vfree_atomic+0x60/0xe0
    scs_free+0x1dc/0x1fc
    scs_release+0xa4/0xd4
    free_task+0x30/0xe4
    __put_task_struct+0x1ec/0x2e0
    delayed_put_task_struct+0x5c/0xa0
    rcu_do_batch+0x62c/0x8a0
    rcu_core+0x60c/0xc14
    rcu_core_si+0x14/0x24
    __do_softirq+0x19c/0x68c
    irq_exit+0x118/0x2dc
    handle_domain_irq+0xcc/0x134
    gic_handle_irq+0x7c/0x1bc
    call_on_irq_stack+0x40/0x70
    do_interrupt_handler+0x78/0x9c
    el1_interrupt+0x34/0x60
    el1h_64_irq_handler+0x1c/0x2c
    el1h_64_irq+0x78/0x7c
    _raw_spin_unlock_irqrestore+0x40/0xcc
    sched_fork+0x4f0/0xb00
    copy_process+0xacc/0x3648
    kernel_clone+0x168/0x534
    kernel_thread+0x13c/0x1b0
    kthreadd+0x2bc/0x400
    ret_from_fork+0x10/0x20

    Memory state around the buggy address:
    ffff8000100b8f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ffff8000100b8f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    >ffff8000100b9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ^
    ffff8000100b9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ffff8000100b9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
    ==================================================================

    Suggested-by: Kuan-Ying Lee <kuan-ying.lee@mediatek.com>
    Acked-by: Will Deacon <will@kernel.org>
    Tested-by: Will Deacon <will@kernel.org>
    Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
    Signed-off-by: Yee Lee <yee.lee@mediatek.com>
    Fixes: a2abe7cbd8fe ("scs: switch to vmapped shadow stacks")
    Link: https://lore.kernel.org/r/20210930081619.30091-1-yee.lee@mediatek.com
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/scs.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/kernel/scs.c b/kernel/scs.c
    index e2a71fc82fa06..579841be88646 100644
    --- a/kernel/scs.c
    +++ b/kernel/scs.c
    @@ -78,6 +78,7 @@ void scs_free(void *s)
    if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)
    return;

    + kasan_unpoison_vmalloc(s, SCS_SIZE);
    vfree_atomic(s);
    }

    --
    2.33.0


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