On 11/30/23 at 09:20pm, fuqiang wang wrote:
>
> On 2023/11/30 15:44, Baoquan He wrote:
> > On 11/27/23 at 10:56am, fuqiang wang wrote:
> > > When the split happened, judge whether mem->nr_ranges is equal to
> > > mem->max_nr_ranges. If it is true, return -ENOMEM.
> > >
> > > The advantage of doing this is that it can avoid array bounds caused by
> > > some bugs. E.g., Before commit 4831be702b95 ("arm64/kexec: Fix missing
> > > extra range for crashkres_low."), reserve both high and low memories for
> > > the crashkernel may cause out of bounds.
> > >
> > > On the other hand, move this code before the split to ensure that the
> > > array will not be changed when return error.
> > If out of array boundary is caused, means the laoding failed, whether
> > the out of boundary happened or not. I don't see how this code change
> > makes sense. Do I miss anything?
> >
> > Thanks
> > Baoquan
> >
> Hi baoquan,
>
> In some configurations, out of bounds may not cause crash_exclude_mem_range()
> returns error, then the load will succeed.
>
> E.g.
> There is a cmem before execute crash_exclude_mem_range():
>
> cmem = {
> max_nr_ranges = 3
> nr_ranges = 2
> ranges = {
> {start = 1, end = 1000}
> {start = 1001, end = 2000}
> }
> }
>
> After executing twice crash_exclude_mem_range() with the start/end params
> 100/200, 300/400 respectively, the cmem will be:
>
> cmem = {
> max_nr_ranges = 3
> nr_ranges = 4 <== nr_ranges > max_nr_ranges
> ranges = {
> {start = 1, end = 99 }
> {start = 201, end = 299 }
> {start = 401, end = 1000}
> {start = 1001, end = 2000} <== OUT OF BOUNDS
> }
> }
Let me borrow your example and copy them here, but I will switch the
order of start/end params 100/200, 300/400 executing at below:
There is a cmem before execute crash_exclude_mem_range():
cmem = {
max_nr_ranges = 3
nr_ranges = 2
ranges = {
{start = 1, end = 1000}
{start = 1001, end = 2000}
}
}
After executing twice crash_exclude_mem_range() with the start/end params
300/400, the cmem will be:
cmem = {
max_nr_ranges = 3
nr_ranges = 3 <== nr_ranges == max_nr_ranges
ranges = {
{start = 1, end = 299 } i=0
{start = 401, end = 1000} i=1
{start = 1001, end = 2000} i=2
}
}
When it's executing the 100/200 excluding, we have:
cmem = {
max_nr_ranges = 3
nr_ranges = 4 <== nr_ranges > max_nr_ranges
ranges = {
{start = 1, end = 99 } i=0
{start = 401, end = 1000}
{start = 1001, end = 2000}
}
}
Then splitting happened, i == 0, then for loop is broken and jump out.
Then we have the condition checking here:
/* Split happened */
if (i == mem->max_nr_ranges - 1)
return -ENOMEM;
Obviously the conditonal checking is incorrect (given the i == 0 in
above case), it should be
/* Split happened */
if (mem->nr_ranges == mem->max_nr_ranges)
return -ENOMEM;
So, now there are two things which need be combed up in
crash_exclude_mem_range():
1) the above conditional check is incorrect, need be fixed;
2) whether we need have the cmem->ranges[] partly changed, or keep it
unchanged when OOB happened;
And also the incorrect handling in crash_setup_memmap_entries():
1) the insufficient array slot in crash_setup_memmap_entries();
2) the uninitialized cmem->max_nr_ranges;
>
> When an out of bounds occurs during the second execution, the function will not
> return error.
>
> Additionally, when the function returns error, means the load failed. It seems
> meaningless to keep the original data unchanged. But in my opinion, this will
> make this function more rigorous and more versatile. (However, I am not sure if
> it is self-defeating and I hope to receive more suggestions).
>
> Thanks
> fuqiang
>
>
> > > Signed-off-by: fuqiang wang <fuqiang.wang@xxxxxxxxxxxx>
> > > ---
> > > kernel/crash_core.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > > index efe87d501c8c..ffdc246cf425 100644
> > > --- a/kernel/crash_core.c
> > > +++ b/kernel/crash_core.c
> > > @@ -611,6 +611,9 @@ int crash_exclude_mem_range(struct crash_mem *mem,
> > > }
> > > if (p_start > start && p_end < end) {
> > > + /* Split happened */
> > > + if (mem->nr_ranges == mem->max_nr_ranges)
> > > + return -ENOMEM;
> > > /* Split original range */
> > > mem->ranges[i].end = p_start - 1;
> > > temp_range.start = p_end + 1;
> > > @@ -626,9 +629,6 @@ int crash_exclude_mem_range(struct crash_mem *mem,
> > > if (!temp_range.end)
> > > return 0;
> > > - /* Split happened */
> > > - if (i == mem->max_nr_ranges - 1)
> > > - return -ENOMEM;
> > > /* Location where new range should go */
> > > j = i + 1;
> > > --
> > > 2.42.0
> > >
> > >
> > > _______________________________________________
> > > kexec mailing list
> > > kexec@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/kexec
> > >
>
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