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Subject: Re: [PATCH] powerpc/64: properly initialise the stackprotector
 canary on SMP.
From:   Abdul Haleem <abdhalee@linux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Mon, 15 Oct 2018 15:03:21 +0530
In-Reply-To: <a2694b8ffeb6c52d1c755d8a7bfaac689c4e1c6d.1539423893.git.christophe.leroy@c-s.fr>
References: <a2694b8ffeb6c52d1c755d8a7bfaac689c4e1c6d.1539423893.git.christophe.leroy@c-s.fr>
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On Sat, 2018-10-13 at 09:45 +0000, Christophe Leroy wrote:
> commit 06ec27aea9fc ("powerpc/64: add stack protector support")
> doesn't initialise the stack canary on SMP secondary CPU's paca,
> leading to the following false positive report from the
> stack protector.
> 
> smp: Bringing up secondary CPUs ...
> Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: __schedule+0x978/0xa80
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.0-rc7-next-20181010-autotest-autotest #1
> Call Trace:
> [c000001fed5b3bf0] [c000000000a0ef3c] dump_stack+0xb0/0xf4 (unreliable)
> [c000001fed5b3c30] [c0000000000f9d68] panic+0x140/0x308
> [c000001fed5b3cc0] [c0000000000f9844] __stack_chk_fail+0x24/0x30
> [c000001fed5b3d20] [c000000000a2c3a8] __schedule+0x978/0xa80
> [c000001fed5b3e00] [c000000000a2c9b4] schedule_idle+0x34/0x60
> [c000001fed5b3e30] [c00000000013d344] do_idle+0x224/0x3d0
> [c000001fed5b3ec0] [c00000000013d6e0] cpu_startup_entry+0x30/0x50
> [c000001fed5b3ef0] [c000000000047f34] start_secondary+0x4d4/0x520
> [c000001fed5b3f90] [c00000000000b370] start_secondary_prolog+0x10/0x14
> 
> This patch properly initialises the stack_canary of the secondary
> idle tasks.
> 
> Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
> Fixes: 06ec27aea9fc ("powerpc/64: add stack protector support")
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/kernel/smp.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 61c1fadbc644..e774d3bf3a03 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -34,6 +34,7 @@
>  #include <linux/topology.h>
>  #include <linux/profile.h>
>  #include <linux/processor.h>
> +#include <linux/random.h>
> 
>  #include <asm/ptrace.h>
>  #include <linux/atomic.h>
> @@ -810,9 +811,16 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
>  {
>  	struct thread_info *ti = task_thread_info(idle);
> 
> +#ifdef CONFIG_STACKPROTECTOR
> +	idle->stack_canary = get_random_canary();
> +#endif
> +
>  #ifdef CONFIG_PPC64
>  	paca_ptrs[cpu]->__current = idle;
>  	paca_ptrs[cpu]->kstack = (unsigned long)ti + THREAD_SIZE - STACK_FRAME_OVERHEAD;
> +#ifdef CONFIG_STACKPROTECTOR
> +	paca_ptrs[cpu]->canary = idle->stack_canary;
> +#endif
>  #endif
>  	ti->cpu = cpu;
>  	secondary_ti = current_set[cpu] = ti;

Thank you Christophe for the fix, Machine boots fine with above patch.

Reported-and-tested-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>


-- 
Regard's

Abdul Haleem
IBM Linux Technology Centre