Re: [PATCH] ARM: mm: Provide better fault message for permission fault

[Kefeng Wang]

Sorry, is_permission_fault() could be used if CONFIG_MMU disabled, will 
resend.

On 2022/9/19 13:11, Kefeng Wang wrote:
> If there is a permission fault in __do_kernel_fault(), we only
> print the generic "paging request" message which don't show
> read, write or execute information, let's provide better fault
> message for them.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
>   arch/arm/mm/fault.c | 35 +++++++++++++++++++++--------------
>   1 file changed, 21 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index 46cccd6bf705..d1b848f0f7ed 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -95,6 +95,19 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
>   
>   	pr_cont("\n");
>   }
> +
> +static inline bool is_permission_fault(unsigned int fsr)
> +{
> +	int fs = fsr_fs(fsr);
> +#ifdef CONFIG_ARM_LPAE
> +	if ((fs & FS_PERM_NOLL_MASK) == FS_PERM_NOLL)
> +		return true;
> +#else
> +	if (fs == FS_L1_PERM || fs == FS_L2_PERM)
> +		return true;
> +#endif
> +	return false;
> +}
>   #else					/* CONFIG_MMU */
>   void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
>   { }
> @@ -137,7 +150,14 @@ __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
>   	/*
>   	 * No handler, we'll have to terminate things with extreme prejudice.
>   	 */
> -	if (addr < PAGE_SIZE) {
> +	if (is_permission_fault(fsr)) {
> +		if (fsr & FSR_WRITE)
> +			msg = "write to read-only memory";
> +		else if (fsr & FSR_LNX_PF)
> +			msg = "execute from non-executable memory";
> +		else
> +			msg = "read from unreadable memory";
> +	} else if (addr < PAGE_SIZE) {
>   		msg = "NULL pointer dereference";
>   	} else {
>   		if (kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
> @@ -204,19 +224,6 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
>   #define VM_FAULT_BADMAP		((__force vm_fault_t)0x010000)
>   #define VM_FAULT_BADACCESS	((__force vm_fault_t)0x020000)
>   
> -static inline bool is_permission_fault(unsigned int fsr)
> -{
> -	int fs = fsr_fs(fsr);
> -#ifdef CONFIG_ARM_LPAE
> -	if ((fs & FS_PERM_NOLL_MASK) == FS_PERM_NOLL)
> -		return true;
> -#else
> -	if (fs == FS_L1_PERM || fs == FS_L2_PERM)
> -		return true;
> -#endif
> -	return false;
> -}
> -
>   static vm_fault_t __kprobes
>   __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int flags,
>   		unsigned long vma_flags, struct pt_regs *regs)