Re: [PATCH] scs: Release kasan vmalloc poison in scs_free process
From: Sami Tolvanen <samitolvanen@google.com>
Date: 2021-09-24 14:32:35
Also in:
linux-mediatek, lkml
Hi, On Thu, Sep 23, 2021 at 2:53 AM [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Yee Lee <redacted> 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 <redacted> --- 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);
Thanks for the patch! I believe I had this in the original vmap SCS series, but Will pointed out that unpoisoning shouldn't be necessary before vfree_atomic() and I don't remember seeing this KASAN error back then. I wonder if something changed there? Either way, the patch looks good to me. Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Sami _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel