Re: [PATCH] module: Refine kmemleak scanned areas

[Vincent Donnefort]

On Mon, Sep 09, 2024 at 09:52:57AM +0100, Catalin Marinas wrote:
> On Mon, Sep 09, 2024 at 08:40:34AM +0100, Vincent Donnefort wrote:
> > On Sat, Sep 07, 2024 at 03:12:13PM +0100, Catalin Marinas wrote:
> > > On Fri, Sep 06, 2024 at 04:38:56PM +0100, Vincent Donnefort wrote:
> > > > commit ac3b43283923 ("module: replace module_layout with module_memory")
> > > > introduced a set of memory regions for the module layout sharing the
> > > > same attributes but didn't update the kmemleak scanned areas which
> > > > intended to limit kmemleak scan to sections containing writable data.
> > > > This means sections such as .text and .rodata are scanned by kmemleak.
> > > > 
> > > > Refine the scanned areas for modules by limiting it to MOD_TEXT and
> > > > MOD_INIT_TEXT mod_mem regions.
> > > > 
> > > > CC: Song Liu <song@xxxxxxxxxx>
> > > > CC: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > > Signed-off-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
> > > > 
> > > > diff --git a/kernel/module/debug_kmemleak.c b/kernel/module/debug_kmemleak.c
> > > > index 12a569d361e8..b4cc03842d70 100644
> > > > --- a/kernel/module/debug_kmemleak.c
> > > > +++ b/kernel/module/debug_kmemleak.c
> > > > @@ -12,19 +12,9 @@
> > > >  void kmemleak_load_module(const struct module *mod,
> > > >  			  const struct load_info *info)
> > > >  {
> > > > -	unsigned int i;
> > > > -
> > > > -	/* only scan the sections containing data */
> > > > -	kmemleak_scan_area(mod, sizeof(struct module), GFP_KERNEL);
> > > > -
> > > > -	for (i = 1; i < info->hdr->e_shnum; i++) {
> > > > -		/* Scan all writable sections that's not executable */
> > > > -		if (!(info->sechdrs[i].sh_flags & SHF_ALLOC) ||
> > > > -		    !(info->sechdrs[i].sh_flags & SHF_WRITE) ||
> > > > -		    (info->sechdrs[i].sh_flags & SHF_EXECINSTR))
> > > > -			continue;
> > > > -
> > > > -		kmemleak_scan_area((void *)info->sechdrs[i].sh_addr,
> > > > -				   info->sechdrs[i].sh_size, GFP_KERNEL);
> > > > +	/* only scan writable, non-executable sections */
> > > > +	for_each_mod_mem_type(type) {
> > > > +		if (type != MOD_DATA && type != MOD_INIT_DATA)
> > > > +			kmemleak_no_scan(mod->mem[type].base);
> > > >  	}
> > > >  }
> > > 
> > > I lost track of how module memory allocation works. Is struct module
> > > still scanned after this change?
> > 
> > That section being RW, it will be part of the MOD_DATA vmalloc and scanned.
> 
> Ah, makes sense. I'm fine with this patch, it simplifies the code now
> that we have mod->mem[type]. I wouldn't say it's a fix, though no
> backporting needed.

Agreed, it's "fixing" because it was scanning unecessary regions, but it's not
worth any backport.

Aside, judging by the size of this function, I am not sure it's worth to keep
a separated file, but the patch that introduced it didn't really explain why so
I kept it that way.

> 
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>

Cheers!

-- 
Vincent