Re: [PATCH v2 2/3] kasan: integrate the common part of two KASAN tag-based modes

[Kuan-Ying Lee]

On Sat, Jun 12, 2021 at 04:42:44PM +0200, Marco Elver wrote:
> On Sat, 12 Jun 2021 at 06:52, Kuan-Ying Lee <kylee0686026@xxxxxxxxx> wrote:
> > 1. Move kasan_get_free_track() and kasan_set_free_info()
> >    into tags.c
> > 2. Move kasan_get_bug_type() to header file
> >
> > Signed-off-by: Kuan-Ying Lee <kylee0686026@xxxxxxxxx>
> > Suggested-by: Marco Elver <elver@xxxxxxxxxx>
> > Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> > Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >  mm/kasan/Makefile         |  4 +--
> >  mm/kasan/hw_tags.c        | 22 ---------------
> >  mm/kasan/report_hw_tags.c |  6 +---
> >  mm/kasan/report_sw_tags.c | 46 +------------------------------
> >  mm/kasan/report_tags.h    | 56 +++++++++++++++++++++++++++++++++++++
> >  mm/kasan/sw_tags.c        | 41 ---------------------------
> >  mm/kasan/tags.c           | 58 +++++++++++++++++++++++++++++++++++++++
> >  7 files changed, 118 insertions(+), 115 deletions(-)
> >  create mode 100644 mm/kasan/report_tags.h
> >  create mode 100644 mm/kasan/tags.c
> [...]
> > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> > index ed5e5b833d61..4ea8c368b5b8 100644
> > --- a/mm/kasan/hw_tags.c
> > +++ b/mm/kasan/hw_tags.c
> > @@ -216,28 +216,6 @@ void __init kasan_init_hw_tags(void)
> >         pr_info("KernelAddressSanitizer initialized\n");
> >  }
> >
> > -void kasan_set_free_info(struct kmem_cache *cache,
> > -                               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -
> > -       alloc_meta = kasan_get_alloc_meta(cache, object);
> > -       if (alloc_meta)
> > -               kasan_set_track(&alloc_meta->free_track[0], GFP_NOWAIT);
> > -}
> > -
> > -struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > -                               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -
> > -       alloc_meta = kasan_get_alloc_meta(cache, object);
> > -       if (!alloc_meta)
> > -               return NULL;
> > -
> > -       return &alloc_meta->free_track[0];
> > -}
> > -
> >  void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
> >  {
> >         /*
> > diff --git a/mm/kasan/report_hw_tags.c b/mm/kasan/report_hw_tags.c
> > index 42b2168755d6..ef5e7378f3aa 100644
> > --- a/mm/kasan/report_hw_tags.c
> > +++ b/mm/kasan/report_hw_tags.c
> > @@ -14,11 +14,7 @@
> >  #include <linux/types.h>
> >
> >  #include "kasan.h"
> > -
> > -const char *kasan_get_bug_type(struct kasan_access_info *info)
> > -{
> > -       return "invalid-access";
> > -}
> > +#include "report_tags.h"
> >
> >  void *kasan_find_first_bad_addr(void *addr, size_t size)
> >  {
> > diff --git a/mm/kasan/report_sw_tags.c b/mm/kasan/report_sw_tags.c
> > index 821a14a19a92..d965a170083e 100644
> > --- a/mm/kasan/report_sw_tags.c
> > +++ b/mm/kasan/report_sw_tags.c
> > @@ -26,51 +26,7 @@
> >
> >  #include <asm/sections.h>
> >
> > -#include "kasan.h"
> > -#include "../slab.h"
> > -
> > -const char *kasan_get_bug_type(struct kasan_access_info *info)
> > -{
> > -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> > -       struct kasan_alloc_meta *alloc_meta;
> > -       struct kmem_cache *cache;
> > -       struct page *page;
> > -       const void *addr;
> > -       void *object;
> > -       u8 tag;
> > -       int i;
> > -
> > -       tag = get_tag(info->access_addr);
> > -       addr = kasan_reset_tag(info->access_addr);
> > -       page = kasan_addr_to_page(addr);
> > -       if (page && PageSlab(page)) {
> > -               cache = page->slab_cache;
> > -               object = nearest_obj(cache, page, (void *)addr);
> > -               alloc_meta = kasan_get_alloc_meta(cache, object);
> > -
> > -               if (alloc_meta) {
> > -                       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> > -                               if (alloc_meta->free_pointer_tag[i] == tag)
> > -                                       return "use-after-free";
> > -                       }
> > -               }
> > -               return "out-of-bounds";
> > -       }
> > -
> > -#endif
> > -       /*
> > -        * If access_size is a negative number, then it has reason to be
> > -        * defined as out-of-bounds bug type.
> > -        *
> > -        * Casting negative numbers to size_t would indeed turn up as
> > -        * a large size_t and its value will be larger than ULONG_MAX/2,
> > -        * so that this can qualify as out-of-bounds.
> > -        */
> > -       if (info->access_addr + info->access_size < info->access_addr)
> > -               return "out-of-bounds";
> > -
> > -       return "invalid-access";
> > -}
> > +#include "report_tags.h"
> >
> >  void *kasan_find_first_bad_addr(void *addr, size_t size)
> >  {
> > diff --git a/mm/kasan/report_tags.h b/mm/kasan/report_tags.h
> > new file mode 100644
> > index 000000000000..4f740d4d99ee
> > --- /dev/null
> > +++ b/mm/kasan/report_tags.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __MM_KASAN_REPORT_TAGS_H
> > +#define __MM_KASAN_REPORT_TAGS_H
> > +
> > +#include "kasan.h"
> > +#include "../slab.h"
> > +
> > +#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> > +const char *kasan_get_bug_type(struct kasan_access_info *info)
> > +{
> [...]
> > +       /*
> > +        * If access_size is a negative number, then it has reason to be
> > +        * defined as out-of-bounds bug type.
> > +        *
> > +        * Casting negative numbers to size_t would indeed turn up as
> > +        * a large size_t and its value will be larger than ULONG_MAX/2,
> > +        * so that this can qualify as out-of-bounds.
> > +        */
> > +       if (info->access_addr + info->access_size < info->access_addr)
> > +               return "out-of-bounds";
> 
> This seems to change behaviour for SW_TAGS because it was there even
> if !CONFIG_KASAN_TAGS_IDENTIFY. Does it still work as before?
> 

You are right. It will change the behavior.
However, I think that if !CONFIG_KASAN_TAG_IDENTIFY, it should be reported
"invalid-access".

Or is it better to keep it in both conditions?

> > +
> > +       return "invalid-access";
> > +}
> > +#else
> > +const char *kasan_get_bug_type(struct kasan_access_info *info)
> > +{
> > +       return "invalid-access";
> > +}
> > +#endif
> > +
> > +#endif
> > diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> > index dd05e6c801fa..bd3f540feb47 100644
> > --- a/mm/kasan/sw_tags.c
> > +++ b/mm/kasan/sw_tags.c
> > @@ -167,47 +167,6 @@ void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
> >  }
> >  EXPORT_SYMBOL(__hwasan_tag_memory);
> >
> > -void kasan_set_free_info(struct kmem_cache *cache,
> > -                               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -       u8 idx = 0;
> > -
> > -       alloc_meta = kasan_get_alloc_meta(cache, object);
> > -       if (!alloc_meta)
> > -               return;
> > -
> > -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> > -       idx = alloc_meta->free_track_idx;
> > -       alloc_meta->free_pointer_tag[idx] = tag;
> > -       alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
> > -#endif
> > -
> > -       kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
> > -}
> > -
> > -struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > -                               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -       int i = 0;
> > -
> > -       alloc_meta = kasan_get_alloc_meta(cache, object);
> > -       if (!alloc_meta)
> > -               return NULL;
> > -
> > -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> > -       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> > -               if (alloc_meta->free_pointer_tag[i] == tag)
> > -                       break;
> > -       }
> > -       if (i == KASAN_NR_FREE_STACKS)
> > -               i = alloc_meta->free_track_idx;
> > -#endif
> > -
> > -       return &alloc_meta->free_track[i];
> > -}
> > -
> >  void kasan_tag_mismatch(unsigned long addr, unsigned long access_info,
> >                         unsigned long ret_ip)
> >  {
> > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> > new file mode 100644
> > index 000000000000..9c33c0ebe1d1
> > --- /dev/null
> > +++ b/mm/kasan/tags.c
> > @@ -0,0 +1,58 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * This file contains common tag-based KASAN code.
> > + *
> > + * Author: Kuan-Ying Lee <kylee0686026@xxxxxxxxx>
> 
> We appreciate your work on this, but this is misleading. Because you
> merely copied/moved the code, have a look what sw_tags.c says -- that
> should either be preserved, or we add nothing here.
> 
> I prefer to add nothing or the bare minimum (e.g. if the company
> requires a Copyright line) for non-substantial additions because this
> stuff becomes out-of-date fast and just isn't useful at all. 'git log'
> is the source of truth.

This was my first time to upload a new file.
Thanks for the suggestions. :)
I will remove this author tag and wait for Greg's process advice.

> 
> Cc'ing Greg for process advice. For moved code, does it have to
> preserve the original Copyright line if there was one?
> 
> Thanks,
> -- Marco