[PATCH] x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()

[PATCH] x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()

[Yuntao Wang]

kernel_ident_mapping_init() takes an exclusive memory range [pstart, pend)
where pend is not included in the range, while res represents an inclusive
memory range [start, end] where end is considered part of the range.

Therefore, passing res->end directly to kernel_ident_mapping_init() is
incorrect, the correct end address should be `res->end + 1`.

Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
---
 arch/x86/kernel/machine_kexec_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 6f8df998890e..bc0a5348b4a6 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -44,7 +44,7 @@ static int mem_region_callback(struct resource *res, void *arg)
 	struct init_pgtable_data *data = arg;
 
 	return kernel_ident_mapping_init(data->info, data->level4p,
-					 res->start, res->end);
+					 res->start, res->end + 1);
 }
 
 static int
-- 
2.43.0

Re: [PATCH] x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()

[Andrew Morton]

On Thu, 21 Dec 2023 18:17:02 +0800 Yuntao Wang <ytcoode@gmail.com> wrote:

> kernel_ident_mapping_init() takes an exclusive memory range [pstart, pend)
> where pend is not included in the range, while res represents an inclusive
> memory range [start, end] where end is considered part of the range.
> 
> Therefore, passing res->end directly to kernel_ident_mapping_init() is
> incorrect, the correct end address should be `res->end + 1`.
> 
> ...
>
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -44,7 +44,7 @@ static int mem_region_callback(struct resource *res, void *arg)
>  	struct init_pgtable_data *data = arg;
>  
>  	return kernel_ident_mapping_init(data->info, data->level4p,
> -					 res->start, res->end);
> +					 res->start, res->end + 1);
>  }

Thanks.  When fixing a bug, please always full describe the
userspace-visible effects of that bug.

In this case I'm assuming "none", due to kernel_ident_mapping_init()'s
upward rounding of the address?

Re: [PATCH] x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()

[Yuntao Wang]

On Thu, 21 Dec 2023 14:03:00 -0800, Andrew Morton <akpm@linux-foundation.org> wrote:

> On Thu, 21 Dec 2023 18:17:02 +0800 Yuntao Wang <ytcoode@gmail.com> wrote:
> 
> > kernel_ident_mapping_init() takes an exclusive memory range [pstart, pend)
> > where pend is not included in the range, while res represents an inclusive
> > memory range [start, end] where end is considered part of the range.
> > 
> > Therefore, passing res->end directly to kernel_ident_mapping_init() is
> > incorrect, the correct end address should be `res->end + 1`.
> > 
> > ...
> >
> > --- a/arch/x86/kernel/machine_kexec_64.c
> > +++ b/arch/x86/kernel/machine_kexec_64.c
> > @@ -44,7 +44,7 @@ static int mem_region_callback(struct resource *res, void *arg)
> >  	struct init_pgtable_data *data = arg;
> >  
> >  	return kernel_ident_mapping_init(data->info, data->level4p,
> > -					 res->start, res->end);
> > +					 res->start, res->end + 1);
> >  }
> 
> Thanks.  When fixing a bug, please always full describe the
> userspace-visible effects of that bug.
> 
> In this case I'm assuming "none", due to kernel_ident_mapping_init()'s
> upward rounding of the address?

Passing [start, end] rather than [start, end+1) to kernel_ident_mapping_init()
may result in the identity mapping for the end address not being set up.

For example, when res->start is equal to res->end, kernel_ident_mapping_init()
will not establish any identity mapping. Similarly, when the value of res->end
is a multiple of 2M and the page table maps 2M pages, kernel_ident_mapping_init()
will also not set up identity mapping for res->end.