Re: ppc elf_map breakage with MAP_FIXED_NOREPLACE

[Anshuman Khandual]

On 02/01/2018 07:18 PM, Michal Hocko wrote:
> On Thu 01-02-18 08:43:34, Anshuman Khandual wrote:
> [...]
>> $dmesg | grep elf_brk
>> [    9.571192] elf_brk 10030328 elf_bss 10030000
>>
>> static int load_elf_binary(struct linux_binprm *bprm)
>> ---------------------
>>
>> 	if (unlikely (elf_brk > elf_bss)) {
>> 			unsigned long nbyte;
>> 	            
>> 			/* There was a PT_LOAD segment with p_memsz > p_filesz
>> 			   before this one. Map anonymous pages, if needed,
>> 			   and clear the area.  */
>> 			retval = set_brk(elf_bss + load_bias,
>> 					 elf_brk + load_bias,
>> 					 bss_prot);
>>
>>
>> ---------------------
> 
> Just a blind shot... Does the following make any difference?
> ---
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 021fe78998ea..04b24d00c911 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -895,7 +895,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  	   the correct location in memory. */
>  	for(i = 0, elf_ppnt = elf_phdata;
>  	    i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
> -		int elf_prot = 0, elf_flags;
> +		int elf_prot = 0, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
>  		unsigned long k, vaddr;
>  		unsigned long total_size = 0;
>  
> @@ -927,6 +927,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  					 */
>  				}
>  			}
> +			elf_fixed = MAP_FIXED;
>  		}
>  
>  		if (elf_ppnt->p_flags & PF_R)
> @@ -944,7 +945,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  		 * the ET_DYN load_addr calculations, proceed normally.
>  		 */
>  		if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
> -			elf_flags |= MAP_FIXED_NOREPLACE;
> +			elf_flags |= elf_fixed;
>  		} else if (loc->elf_ex.e_type == ET_DYN) {
>  			/*
>  			 * This logic is run once for the first LOAD Program
> @@ -980,7 +981,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  				load_bias = ELF_ET_DYN_BASE;
>  				if (current->flags & PF_RANDOMIZE)
>  					load_bias += arch_mmap_rnd();
> -				elf_flags |= MAP_FIXED_NOREPLACE;
> +				elf_flags |= elf_fixed;
>  			} else
>  				load_bias = 0;
>  
> 

Yeah, it does solve the problem on mmotm-2018-01-25-16-20.