[PATCH] ARC: fix CONFIG_HARDENED_USERCOPY

[Kees Cook]

On Wed, Jun 09, 2021 at 03:12:11PM -0700, Vineet Gupta wrote:
> Currently enabling this triggers a warning
> 
> | usercopy: Kernel memory overwrite attempt detected to kernel text (offset 155633, size 11)!
> | usercopy: BUG: failure at mm/usercopy.c:99/usercopy_abort()!
> |
> |gcc generated __builtin_trap
> |Path: /bin/busybox
> |CPU: 0 PID: 84 Comm: init Not tainted 5.4.22
> |
> |[ECR ]: 0x00090005 => gcc generated __builtin_trap
> |[EFA ]: 0x9024fcaa
> |[BLINK ]: usercopy_abort+0x8a/0x8c
> |[ERET ]: memfd_fcntl+0x0/0x470
> |[STAT32]: 0x80080802 : IE K
> |BTA: 0x901ba38c SP: 0xbe161ecc FP: 0xbf9fe950
> |LPS: 0x90677408 LPE: 0x9067740c LPC: 0x00000000
> |r00: 0x0000003c r01: 0xbf0ed280 r02: 0x00000000
> |r03: 0xbe15fa30 r04: 0x00d2803e r05: 0x00000000
> |r06: 0x675d7000 r07: 0x00000000 r08: 0x675d9c00
> |r09: 0x00000000 r10: 0x0000035c r11: 0x61206572
> |r12: 0x9024fcaa r13: 0x0000000b r14: 0x0000000b
> |r15: 0x00000000 r16: 0x90169ffc r17: 0x90168000
> |r18: 0x00000000 r19: 0xbf092010 r20: 0x00000001
> |r21: 0x00000011 r22: 0x5ffffff1 r23: 0x90169ff1
> |r24: 0xbe196c00 r25: 0xbf0ed280
> |
> |Stack Trace:
> | memfd_fcntl+0x0/0x470
> | usercopy_abort+0x8a/0x8c
> | __check_object_size+0x10e/0x138
> | copy_strings+0x1f4/0x38c
> | __do_execve_file+0x352/0x848
> | EV_Trap+0xcc/0xd0

What was the root cause here? Was it that the init section gets freed
and reused for kmalloc?

> 
> Fixes: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/15
> Reported-by: Evgeniy Didin <didin at synopsys.com>
> Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
> ---
>  arch/arc/kernel/vmlinux.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arc/kernel/vmlinux.lds.S b/arch/arc/kernel/vmlinux.lds.S
> index 33ce59d91461..e2146a8da195 100644
> --- a/arch/arc/kernel/vmlinux.lds.S
> +++ b/arch/arc/kernel/vmlinux.lds.S
> @@ -57,7 +57,6 @@ SECTIONS
>  	.init.ramfs : { INIT_RAM_FS }
>  
>  	. = ALIGN(PAGE_SIZE);
> -	_stext = .;
>  
>  	HEAD_TEXT_SECTION
>  	INIT_TEXT_SECTION(L1_CACHE_BYTES)
> @@ -83,6 +82,7 @@ SECTIONS
>  
>  	.text : {
>  		_text = .;
> +		_stext = .;
>  		TEXT_TEXT
>  		SCHED_TEXT
>  		CPUIDLE_TEXT
> -- 
> 2.25.1
> 

-- 
Kees Cook