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SubjectRe: [PATCH] scs: Release kasan vmalloc poison in scs_free process
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On Thu, 2021-09-23 at 17:53 +0800, yee.lee@mediatek.com wrote:
> From: Yee Lee <yee.lee@mediatek.com>
>
> Since scs allocation has been 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-(skip)
> 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
> ==================================================================
>
> CC: Matthias Brugger <matthias.bgg@gmail.com>
> CC: Will Deacon <will@kernel.org>
> CC: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> ---
> kernel/scs.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/scs.c b/kernel/scs.c
> index e2a71fc82fa0..25c0d8e416e6 100644
> --- a/kernel/scs.c
> +++ b/kernel/scs.c
> @@ -68,6 +68,7 @@ void scs_free(void *s)
>
> __scs_account(s, -1);
>
> + kasan_unpoison_vmalloc(s, SCS_SIZE);
> /*
> * We cannot sleep as this can be called in interrupt context,
> * so use this_cpu_cmpxchg to update the cache, and
> vfree_atomic

I'm not sure if we need to add kasan_unpoison_vmalloc() and
kasan_poison_vmalloc() in this file.

As far as I know, vmalloc() and vfree() will do these two functions.

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