[PATCH] makedumpfile: memset() in cyclic bitmap initialization introduce segment fault

[Atsushi Kumagai]

On 2013/12/20 10:09:23, kexec <kexec-bounces at lists.infradead.org> wrote:
> (2013/12/18 22:34), WANG Chao wrote:
> > We are using memset() to improve performance when creating 1st and 2nd
> > bitmap. After doing round up the pfn_start and round down pfn_end, it's
> > possible that pfn_start_roundup is greater than pfn_end_round. A segment
> > fault could happen in that case because memset is taking roughly the
> > value of (pfn_end_round << 3 - pfn_start_roundup << 3 ), which is
> > negative, as its third argument.
> >
> > So we can skip the memset if start is greater than end. It's safe
> > because we will set bit for the round up part and also round down part.
> >
> > Actually this happens on my EFI virtual machine:
> >
> > cat /proc/iomem:
> > 00000000-00000fff : reserved
> > 00001000-0009ffff : System RAM
> > 000a0000-000bffff : PCI Bus 0000:00
> > 000f0000-000fffff : System ROM
> > 00100000-3d162017 : System RAM
> >    01000000-015cab9b : Kernel code
> >    015cab9c-019beb3f : Kernel data
> >    01b4f000-01da9fff : Kernel bss
> >    30000000-37ffffff : Crash kernel
> > 3d162018-3d171e57 : System RAM
> > 3d171e58-3d172017 : System RAM
> > 3d172018-3d17ae57 : System RAM
> > 3d17ae58-3dc10fff : System RAM
> > 3dc11000-3dc18fff : reserved
> > 3dc19000-3dc41fff : System RAM
> > 3dc42000-3ddcefff : reserved
> > 3ddcf000-3f7fefff : System RAM
> > 3f7ff000-3f856fff : reserved
> > [..]
> >
> > gdb ./makedumpfile core
> > (gdb) bt full
> > [..]
> >   #1  0x000000000042775d in create_1st_bitmap_cyclic () at makedumpfile.c:4543
> >          i = 0x5
> >          pfn = 0x3d190
> >          phys_start = 0x3d18ee58
> >          phys_end = 0x3d18f018
> >          pfn_start = 0x3d18e
> >          pfn_end = 0x3d18f
> >          pfn_start_roundup = 0x3d190
> >          pfn_end_round = 0x3d188
> >          pfn_start_byte = 0x7a32
> >          pfn_end_byte = 0x7a31
> > [..]
> > (gdb) list makedumpfile.c:4543
> > 4538					return FALSE;
> > 4539
> > 4540			pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
> > 4541			pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
> > 4542
> > 4543			memset(info->partial_bitmap2 + pfn_start_byte,
> > 4544			       0xff,
> > 4545			       pfn_end_byte - pfn_start_byte);
> > 4546
> > 4547			for (pfn = pfn_end_round; pfn < pfn_end; ++pfn)
> >
> > Signed-off-by: WANG Chao <chaowang at redhat.com>
> > ---
> >   makedumpfile.c | 18 +++++++++++-------
> >   1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/makedumpfile.c b/makedumpfile.c
> > index 23251a1..ef08d91 100644
> > --- a/makedumpfile.c
> > +++ b/makedumpfile.c
> > @@ -4435,11 +4435,13 @@ create_1st_bitmap_cyclic()
> >   		pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
> >   		pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
> >
> > -		memset(info->partial_bitmap1 + pfn_start_byte,
> > -		       0xff,
> > -		       pfn_end_byte - pfn_start_byte);
> > +		if (pfn_start_byte < pfn_end_byte) {
> > +			memset(info->partial_bitmap1 + pfn_start_byte,
> > +			       0xff,
> > +			       pfn_end_byte - pfn_start_byte);
> >
> > -		pfn_bitmap1 += (pfn_end_byte - pfn_start_byte) * BITPERBYTE;
> > +			pfn_bitmap1 += (pfn_end_byte - pfn_start_byte) * BITPERBYTE;
> > +		}
> >
> >   		for (pfn = pfn_end_round; pfn < pfn_end; pfn++) {
> >   			if (set_bit_on_1st_bitmap(pfn))
> > @@ -4540,9 +4542,11 @@ initialize_2nd_bitmap_cyclic(void)
> >   		pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
> >   		pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
> >
> > -		memset(info->partial_bitmap2 + pfn_start_byte,
> > -		       0xff,
> > -		       pfn_end_byte - pfn_start_byte);
> > +		if (pfn_start_byte < pfn_end_byte) {
> > +			memset(info->partial_bitmap2 + pfn_start_byte,
> > +			       0xff,
> > +			       pfn_end_byte - pfn_start_byte);
> > +		}
> >
> >   		for (pfn = pfn_end_round; pfn < pfn_end; ++pfn)
> >   			if (!set_bit_on_2nd_bitmap_for_kernel(pfn))
> >
> 
> Acked-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>

Thanks, I'll merge this patch into v1.5.6.

Atsushi Kumagai