Re: [PATCH v2] scs: Release kasan vmalloc poison in scs_free process

[Will Deacon]

On Thu, Sep 30, 2021 at 04:16:13PM +0800, yee.lee@xxxxxxxxxxxx wrote:
> From: Yee Lee <yee.lee@xxxxxxxxxxxx>
> 
> 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
>  ==================================================================

Thanks, I'll take this via the arm64 tree as we're the only use of SCS.

One thing for future:

> Suggested-by: Kuan-Ying Lee <kuan-ying.lee@xxxxxxxxxxxx>
> Reviewd-by: Will Deacon <will@xxxxxxxxxx>

I gave an "Acked-by" and a "Tested-by" at [1], so those are the tags you
should be using. Please don't convert them into a "Reviewed-by".

> Reviewd-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

This should be "Reviewed-by" (you have a typo).

Anyway, I'll fix these locally, no need to resend this time.

Will

[1] https://lore.kernel.org/r/20210929115447.GA21631@willie-the-truck