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

[Yee Lee]

Got it. Thank you.

Yee

On Thu, 2021-09-30 at 09:35 +0100, Will Deacon wrote:
> 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://urldefense.com/v3/__https://lore.kernel.org/r/20210929115447.GA21631@willie-the-truck__;!!CTRNKA9wMg0ARbw!yjJi1VvoIbI7CZQJplT_jdN087Pkk6pzXAZ12_FpegZzaUEQutkzBjX85rub_NI$
>