Re: [PATCH v4 1/2] binfmt_flat: allow not offsetting data start

[Greg Ungerer <gerg@linux-m68k.org>]

On 17/4/21 2:54 pm, Damien Le Moal wrote:
> On 2021/04/17 13:52, Greg Ungerer wrote:
>>
>> On 17/4/21 11:10 am, Damien Le Moal wrote:
>>> Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset
>>> the data start"") restored offsetting the start of the data section by
>>> a number of words defined by MAX_SHARED_LIBS. As a result, since
>>> MAX_SHARED_LIBS is never 0, a gap between the text and data sections
>>> always exists. For architectures which cannot support a such gap
>>> between the text and data sections (e.g. riscv nommu), flat binary
>>> programs cannot be executed.
>>>
>>> To allow an architecture to request no data start offset to allow for
>>> contiguous text and data sections for binaries flagged with
>>> FLAT_FLAG_RAM, introduce the new config option
>>> CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET. Using this new option, the
>>> macro DATA_START_OFFSET_WORDS is conditionally defined in binfmt_flat.c
>>> to MAX_SHARED_LIBS for architectures tolerating or needing the data
>>> start offset (CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET disabled case)
>>> and to 0 when CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET is enabled.
>>> DATA_START_OFFSET_WORDS is used in load_flat_file() to calculate the
>>> data section length and start position.
>>>
>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>>> ---
>>>    fs/Kconfig.binfmt |  3 +++
>>>    fs/binfmt_flat.c  | 19 ++++++++++++++-----
>>>    2 files changed, 17 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
>>> index c6f1c8c1934e..06fb7a93a1bd 100644
>>> --- a/fs/Kconfig.binfmt
>>> +++ b/fs/Kconfig.binfmt
>>> @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK
>>>    config BINFMT_FLAT_OLD_ALWAYS_RAM
>>>    	bool
>>>    
>>> +config BINFMT_FLAT_NO_DATA_START_OFFSET
>>> +	bool
>>> +
>>>    config BINFMT_FLAT_OLD
>>>    	bool "Enable support for very old legacy flat binaries"
>>>    	depends on BINFMT_FLAT
>>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
>>> index b9c658e0548e..1dc68dfba3e0 100644
>>> --- a/fs/binfmt_flat.c
>>> +++ b/fs/binfmt_flat.c
>>> @@ -74,6 +74,12 @@
>>>    #define	MAX_SHARED_LIBS			(1)
>>>    #endif
>>>    
>>> +#ifdef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
>>> +#define DATA_START_OFFSET_WORDS		(0)
>>> +#else
>>> +#define DATA_START_OFFSET_WORDS		(MAX_SHARED_LIBS)
>>> +#endif
>>> +
>>>    struct lib_info {
>>>    	struct {
>>>    		unsigned long start_code;		/* Start of text segment */
>>> @@ -560,6 +566,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    	 * it all together.
>>>    	 */
>>>    	if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) {
>>> +
>>
>> Random white space change...
>> Don't worry about re-spinning though, I will just edit this chunk out.
> 
> Oops. Sorry about that. I should have better checked :)
> 
>>
>>
>>>    		/*
>>>    		 * this should give us a ROM ptr,  but if it doesn't we don't
>>>    		 * really care
>>> @@ -576,7 +583,8 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    			goto err;
>>>    		}
>>>    
>>> -		len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long);
>>> +		len = data_len + extra +
>>> +			DATA_START_OFFSET_WORDS * sizeof(unsigned long);
>>>    		len = PAGE_ALIGN(len);
>>>    		realdatastart = vm_mmap(NULL, 0, len,
>>>    			PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0);
>>> @@ -591,7 +599,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    			goto err;
>>>    		}
>>>    		datapos = ALIGN(realdatastart +
>>> -				MAX_SHARED_LIBS * sizeof(unsigned long),
>>> +				DATA_START_OFFSET_WORDS * sizeof(unsigned long),
>>>    				FLAT_DATA_ALIGN);
>>>    
>>>    		pr_debug("Allocated data+bss+stack (%u bytes): %lx\n",
>>> @@ -622,7 +630,8 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    		memp_size = len;
>>>    	} else {
>>>    
>>> -		len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32);
>>> +		len = text_len + data_len + extra +
>>> +			DATA_START_OFFSET_WORDS * sizeof(u32);
>>>    		len = PAGE_ALIGN(len);
>>>    		textpos = vm_mmap(NULL, 0, len,
>>>    			PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0);
>>> @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    
>>>    		realdatastart = textpos + ntohl(hdr->data_start);
>>>    		datapos = ALIGN(realdatastart +
>>> -				MAX_SHARED_LIBS * sizeof(u32),
>>> +				DATA_START_OFFSET_WORDS * sizeof(u32),
>>>    				FLAT_DATA_ALIGN);
>>>    
>>>    		reloc = (__be32 __user *)
>>> @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>>    			ret = result;
>>>    			pr_err("Unable to read code+data+bss, errno %d\n", ret);
>>>    			vm_munmap(textpos, text_len + data_len + extra +
>>> -				MAX_SHARED_LIBS * sizeof(u32));
>>> +				  DATA_START_OFFSET_WORDS * sizeof(u32));
>>>    			goto err;
>>>    		}
>>>    	}
>>>
>>
>> Thanks, otherwise looks good.
>>
>> Acked-by: Greg Ungerer <gerg@linux-m68k.org>
>>
>> I will push this into my m68knommu tree, for-next branch.
>> I just carry the flat format changes in that tree now to make my life easier.
> 
> Great. Thanks !
> Are you taking both patches or should Plamer take the riscv Kconfig change
> through his tree ?

I am happy to take both.
Palmer?

Regards
Greg