Re: [PATCH V2 1/3] riscv: Fixup static_obj() fail

[Aurelien Jarno]

Hi,

On 2020-06-27 13:57, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> 
> When enable LOCKDEP, static_obj() will cause error. Because some
> __initdata static variables is before _stext:
> 
> static int static_obj(const void *obj)
> {
>         unsigned long start = (unsigned long) &_stext,
>                       end   = (unsigned long) &_end,
>                       addr  = (unsigned long) obj;
> 
>         /*
>          * static variable?
>          */
>         if ((addr >= start) && (addr < end))
>                 return 1;
> 
> [    0.067192] INFO: trying to register non-static key.
> [    0.067325] the code is fine but needs lockdep annotation.
> [    0.067449] turning off the locking correctness validator.
> [    0.067718] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.7.0-rc7-dirty #44
> [    0.067945] Call Trace:
> [    0.068369] [<ffffffe00020323c>] walk_stackframe+0x0/0xa4
> [    0.068506] [<ffffffe000203422>] show_stack+0x2a/0x34
> [    0.068631] [<ffffffe000521e4e>] dump_stack+0x94/0xca
> [    0.068757] [<ffffffe000255a4e>] register_lock_class+0x5b8/0x5bc
> [    0.068969] [<ffffffe000255abe>] __lock_acquire+0x6c/0x1d5c
> [    0.069101] [<ffffffe0002550fe>] lock_acquire+0xae/0x312
> [    0.069228] [<ffffffe000989a8e>] _raw_spin_lock_irqsave+0x40/0x5a
> [    0.069357] [<ffffffe000247c64>] complete+0x1e/0x50
> [    0.069479] [<ffffffe000984c38>] rest_init+0x1b0/0x28a
> [    0.069660] [<ffffffe0000016a2>] 0xffffffe0000016a2
> [    0.069779] [<ffffffe000001b84>] 0xffffffe000001b84
> [    0.069953] [<ffffffe000001092>] 0xffffffe000001092
> 
> static __initdata DECLARE_COMPLETION(kthreadd_done);
> 
> noinline void __ref rest_init(void)
> {
> 	...
> 	complete(&kthreadd_done);
> 
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/kernel/vmlinux.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index e6f8016..f3586e3 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -22,6 +22,7 @@ SECTIONS
>  	/* Beginning of code and text segment */
>  	. = LOAD_OFFSET;
>  	_start = .;
> +	_stext = .;
>  	HEAD_TEXT_SECTION
>  	. = ALIGN(PAGE_SIZE);
>  
> @@ -54,7 +55,6 @@ SECTIONS
>  	. = ALIGN(SECTION_ALIGN);
>  	.text : {
>  		_text = .;
> -		_stext = .;
>  		TEXT_TEXT
>  		SCHED_TEXT
>  		CPUIDLE_TEXT


This patch has been backported to kernel 5.8.4. This causes the kernel
to crash when trying to execute the init process:

[    3.484586] AppArmor: AppArmor sha1 policy hashing enabled
[    4.749835] Freeing unused kernel memory: 492K
[    4.752017] Run /init as init process
[    4.753571] usercopy: Kernel memory overwrite attempt detected to kernel text (offset 507879, size 11)!
[    4.754838] ------------[ cut here ]------------
[    4.755651] kernel BUG at mm/usercopy.c:99!
[    4.756445] Kernel BUG [#1]
[    4.756815] Modules linked in:
[    4.757542] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.8.0-1-riscv64 #1 Debian 5.8.7-1
[    4.758372] epc: ffffffe0003b5120 ra : ffffffe0003b5120 sp : ffffffe07f783ca0
[    4.758960]  gp : ffffffe000cc7230 tp : ffffffe07f77cec0 t0 : ffffffe000cdafc0
[    4.759772]  t1 : 0000000000000064 t2 : 0000000000000000 s0 : ffffffe07f783cf0
[    4.760534]  s1 : ffffffe00095d780 a0 : 000000000000005b a1 : 0000000000000020
[    4.761309]  a2 : 0000000000000005 a3 : 0000000000000000 a4 : ffffffe000c1f340
[    4.761848]  a5 : ffffffe000c1f340 a6 : 0000000000000000 a7 : 0000000000000087
[    4.762684]  s2 : ffffffe000941848 s3 : 000000000007bfe7 s4 : 000000000000000b
[    4.763500]  s5 : 0000000000000000 s6 : ffffffe00091cc00 s7 : fffffffffffff000
[    4.764376]  s8 : 0000003ffffff000 s9 : ffffffe0769f3200 s10: 000000000000000b
[    4.765208]  s11: ffffffe07d548c40 t3 : 0000000000000000 t4 : 000000000001dcd0
[    4.766059]  t5 : ffffffe000cc8510 t6 : ffffffe000cd64aa
[    4.766712] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003
[    4.768308] ---[ end trace 1f8e733e834d4c3e ]---
[    4.769129] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[    4.770070] SMP: stopping secondary CPUs
[    4.771110] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---

Note that this is with CONFIG_HARDENED_USERCOPY=y

Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@xxxxxxxxxxx                 http://www.aurel32.net