Re: [PATCH] kexec: avoid out of bounds in crash_exclude_mem_range()

[fuqiang wang]

在 2023/12/19 13:29, Yuntao Wang 写道:
> On Tue, 19 Dec 2023 11:50:32 +0800, fuqiang wang <fuqiang.wang@xxxxxxxxxxxx> wrote:
> > 在 2023/12/19 10:47, Yuntao Wang 写道:
> >
> > > Hi fuqiang,
> > >
> > > Yesterday, I posted two patches that happen to address the bugs you an Baoquan
> > > are currently discussing here, I wasn't aware that you both were also working
> > > on fixing these issues.
> > >
> > > Baoquan suggested I talk to you about it.
> > >
> > > If you're interested, you can take a look at my patches and review them to see
> > > if there are any issues. If everything is fine, and if you're willing, you can
> > > also add a 'Reviewed-by' tag there.
> > >
> > > The following link is for the two patches I posted yesterday:
> > >
> > > https://lore.kernel.org/lkml/20231218081915.24120-3-ytcoode@xxxxxxxxx/t/#u
> > >
> > > Sincerely,
> > > Yuntao
> > Hi Yuntao,
> >
> > I'm glad you've also noticed this issue. But I'm sorry, I want to solve this
> > problem myself because this is my first time posting a patch in the community,
> > and I cherish this opportunity very much.
> I can truly understand your feelings because I still remember how thrilled I
> was when my first patch got merged. So keep it up!

Hi Yuntao,

Thanks for your understanding and encourage. :)

> > I have carefully reviewed your patch. There is some changes where my views differ
> > from yours:
> > diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> > index c92d88680dbf..3be46f4b441e 100644
> > --- a/arch/x86/kernel/crash.c
> > +++ b/arch/x86/kernel/crash.c
> > @@ -282,10 +282,6 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
> >        struct crash_memmap_data cmd;
> >        struct crash_mem *cmem;
> >
> > -    cmem = vzalloc(struct_size(cmem, ranges, 1));
> > -    if (!cmem)
> > -        return -ENOMEM;
> > -
> >        memset(&cmd, 0, sizeof(struct crash_memmap_data));
> >        cmd.params = params;
> >
> > @@ -321,6 +317,11 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
> >        }
> >
> >        /* Exclude some ranges from crashk_res and add rest to memmap */
> > +    cmem = vzalloc(struct_size(cmem, ranges, 1));
> > +    if (!cmem)
> > +        return -ENOMEM;
> > +    cmem->max_nr_ranges = 1;
> > +
> >        ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
> >        if (ret)
> >            goto out;
> >
> > 1. I don't feel very good that you have moved vzalloc() to in front of
> > memmap_exclude_ranges. Because if memory allocation fails, there is no need to
> > do anything else afterwards.
> I moved it here because only memmap_exclude_ranges() and the code below it use cmem.
>
> I think it is a good practice to put related code together, which also improves
> code readability.

Thank you very much for your patient comment. This change does indeed improve
readability. But as a combination of these two, how do you feel about moving
crash_setup_memmap_entries() behind vzalloc().
> > 2. The cmem->max_nr_ranges should be set to 2. Because in
> > memmap_exclude_ranges, a cmem->ranges[] will be filled in and if a split occurs
> > later, another one will be added.
> With the current code, image->elf_load_addr should be equal to crashk_res.start,
> so split will not occur in crash_exclude_mem_range(). Therefore, setting
> cmem->max_nr_ranges to 1 is safe.

The image->elf_load_addr is determined by arch_kexec_locate_mem_hole(), this
function can ensure that the value is within the range of [crashk_res.start,
crashk_res.end), but it seems that it cannot guarantee that its value will
always be equal to crashk_res.start. Perhaps I have some omissions, please
point them out.

Thanks
fuqiang
> > Thanks
> > fuqiang