linux-kernel - Re: [PATCH] riscv: Disable STACKPROTECTOR_PER_TASK if GCC_PLUGIN

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Date:   Fri, 23 Jul 2021 19:13:47 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        guoren@...ux.alibaba.com
Subject: Re: [PATCH] riscv: Disable STACKPROTECTOR_PER_TASK if
 GCC_PLUGIN_RANDSTRUCT is enabled

On 7/23/21 5:58 PM, Palmer Dabbelt wrote:
> On Tue, 06 Jul 2021 09:26:21 PDT (-0700), linux@...ck-us.net wrote:
>> riscv uses the value of TSK_STACK_CANARY to set
>> stack-protector-guard-offset. With GCC_PLUGIN_RANDSTRUCT enabled, that
>> value is non-deterministic, and with riscv:allmodconfig often results
>> in build errors such as
>>
>> cc1: error: '8120' is not a valid offset in '-mstack-protector-guard-offset='
>>
>> Enable STACKPROTECTOR_PER_TASK only if GCC_PLUGIN_RANDSTRUCT is disabled
>> to fix the problem.
>>
>> Fixes: fea2fed201ee5 ("riscv: Enable per-task stack canaries")
>> Cc: Guo Ren <guoren@...ux.alibaba.com>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>>  arch/riscv/Kconfig | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 469a70bd8da6..3afb84fa2190 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -486,6 +486,7 @@ config CC_HAVE_STACKPROTECTOR_TLS
>>
>>  config STACKPROTECTOR_PER_TASK
>>      def_bool y
>> +    depends on !GCC_PLUGIN_RANDSTRUCT
>>      depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_TLS
>>
>>  config PHYS_RAM_BASE_FIXED
> 
> Thanks, this is on fixes.  I do an allmodconfig build and haven't seen these failures, is there something special I need to do to get this working?  I know nothing about GCC plugins...

The problem is seen only randomly. It depends on the value
of TSK_STACK_CANARY in include/generated/asm-offsets.h.
That in turn depends on the location of stack_canary
in struct task_struct. You may have to try several times
from a clean tree to see the problem.

Guenter