Re: [PATCH v3 11/19] x86, boot: Add checking for memcpy

[Baoquan He]

On 03/07/16 at 03:36pm, Kees Cook wrote:
> On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> > From: Yinghai Lu <yinghai@xxxxxxxxxx>
> >
> > parse_elf is using local memcpy to move section to running position.
> > That memcpy actually only support no overlapping case or when dest < src.
> >
> > Add checking in memcpy to find out the wrong case for future use, at
> > that time we will need to have backward memcpy for it.
> >
> > Also add comments in parse_elf about the fact.
> 
> Seems like this would be better to just fix the memcpy to handle the overlap?

Yeah, agree. I will remove the code comment.

> 
> -Kees
> 
> >
> > Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> > ---
> > v2->v3:
> >     Add a declaration for error() since its declaration is in misc.h.
> >     But it's not included in compressed/string.c.
> >
> >  arch/x86/boot/compressed/misc.c   | 14 +++++++-------
> >  arch/x86/boot/compressed/misc.h   |  2 ++
> >  arch/x86/boot/compressed/string.c | 29 +++++++++++++++++++++++++++--
> >  3 files changed, 36 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index dd7ed8a..4b2cd0c 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -114,9 +114,6 @@
> >  #undef memset
> >  #define memzero(s, n)  memset((s), 0, (n))
> >
> > -
> > -static void error(char *m);
> > -
> >  /*
> >   * This is set up by the setup-routine at boot-time
> >   */
> > @@ -243,7 +240,7 @@ void __puthex(unsigned long value)
> >         }
> >  }
> >
> > -static void error(char *x)
> > +void error(char *x)
> >  {
> >         error_putstr("\n\n");
> >         error_putstr(x);
> > @@ -378,9 +375,12 @@ static void parse_elf(void *output)
> >  #else
> >                         dest = (void *)(phdr->p_paddr);
> >  #endif
> > -                       memcpy(dest,
> > -                              output + phdr->p_offset,
> > -                              phdr->p_filesz);
> > +                       /*
> > +                        * simple version memcpy only can work when dest is
> > +                        *   smaller than src or no overlapping.
> > +                        * Here dest is smaller than src always.
> > +                        */
> > +                       memcpy(dest, output + phdr->p_offset, phdr->p_filesz);
> >                         break;
> >                 default: /* Ignore other PT_* */ break;
> >                 }
> > diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> > index 11736a6..39d0e9a 100644
> > --- a/arch/x86/boot/compressed/misc.h
> > +++ b/arch/x86/boot/compressed/misc.h
> > @@ -38,6 +38,8 @@ void __puthex(unsigned long value);
> >  #define error_putstr(__x)  __putstr(__x)
> >  #define error_puthex(__x)  __puthex(__x)
> >
> > +void error(char *x);
> > +
> >  #ifdef CONFIG_X86_VERBOSE_BOOTUP
> >
> >  #define debug_putstr(__x)  __putstr(__x)
> > diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
> > index 00e788b..3a935d0 100644
> > --- a/arch/x86/boot/compressed/string.c
> > +++ b/arch/x86/boot/compressed/string.c
> > @@ -1,7 +1,7 @@
> >  #include "../string.c"
> >
> >  #ifdef CONFIG_X86_32
> > -void *memcpy(void *dest, const void *src, size_t n)
> > +void *__memcpy(void *dest, const void *src, size_t n)
> >  {
> >         int d0, d1, d2;
> >         asm volatile(
> > @@ -15,7 +15,7 @@ void *memcpy(void *dest, const void *src, size_t n)
> >         return dest;
> >  }
> >  #else
> > -void *memcpy(void *dest, const void *src, size_t n)
> > +void *__memcpy(void *dest, const void *src, size_t n)
> >  {
> >         long d0, d1, d2;
> >         asm volatile(
> > @@ -30,6 +30,31 @@ void *memcpy(void *dest, const void *src, size_t n)
> >  }
> >  #endif
> >
> > +extern void error(char *x);
> > +void *memcpy(void *dest, const void *src, size_t n)
> > +{
> > +       unsigned long start_dest, end_dest;
> > +       unsigned long start_src, end_src;
> > +       unsigned long max_start, min_end;
> > +
> > +       if (dest < src)
> > +               return __memcpy(dest, src, n);
> > +
> > +       start_dest = (unsigned long)dest;
> > +       end_dest = (unsigned long)dest + n;
> > +       start_src = (unsigned long)src;
> > +       end_src = (unsigned long)src + n;
> > +       max_start = (start_dest > start_src) ?  start_dest : start_src;
> > +       min_end = (end_dest < end_src) ? end_dest : end_src;
> > +
> > +       if (max_start >= min_end)
> > +               return __memcpy(dest, src, n);
> > +
> > +       error("memcpy does not support overlapping with dest > src!\n");
> > +
> > +       return dest;
> > +}
> > +
> >  void *memset(void *s, int c, size_t n)
> >  {
> >         int i;
> > --
> > 2.5.0
> >
> 
> 
> 
> -- 
> Kees Cook
> Chrome OS & Brillo Security