[PATCH v2] MIPS: kernel: Fix random segmentation faults

[PATCH v2] MIPS: kernel: Fix random segmentation faults

[Thomas Bogendoerfer]

Commit 69896119dc9d ("MIPS: vdso: Switch to generic storage
implementation") switches to a generic vdso storage, which increases
the number of data pages from 1 to 4. But there is only one page
reserved, which causes segementation faults depending where the VDSO
area is randomized to. To fix this use the same size of reservation
and allocation of the VDSO data pages.

Fixes: 69896119dc9d ("MIPS: vdso: Switch to generic storage implementation")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
v2: Don't reserve additionnal VDSO_NR_PAGES, but reserve VDSO_NR_PAGES
    instead of the one page before.
    Reworked description
v1: https://lore.kernel.org/all/20251117191815.69556-1-tsbogend@alpha.franken.de/

 arch/mips/kernel/process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 29191fa1801e..a3101f2268c6 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -692,7 +692,7 @@ unsigned long mips_stack_top(void)
 	/* Space for the VDSO, data page & GIC user page */
 	if (current->thread.abi) {
 		top -= PAGE_ALIGN(current->thread.abi->vdso->size);
-		top -= PAGE_SIZE;
+		top -= VDSO_NR_PAGES * PAGE_SIZE;
 		top -= mips_gic_present() ? PAGE_SIZE : 0;
 
 		/* Space to randomize the VDSO base */
-- 
2.43.0

Re: [PATCH v2] MIPS: kernel: Fix random segmentation faults

[Thomas Weißschuh]

On Thu, Nov 20, 2025 at 01:10:29PM +0100, Thomas Bogendoerfer wrote:
> Commit 69896119dc9d ("MIPS: vdso: Switch to generic storage
> implementation") switches to a generic vdso storage, which increases
> the number of data pages from 1 to 4. But there is only one page
> reserved, which causes segementation faults depending where the VDSO
> area is randomized to. To fix this use the same size of reservation
> and allocation of the VDSO data pages.
> 
> Fixes: 69896119dc9d ("MIPS: vdso: Switch to generic storage implementation")

Thanks!

Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> ---
> v2: Don't reserve additionnal VDSO_NR_PAGES, but reserve VDSO_NR_PAGES
>     instead of the one page before.
>     Reworked description
> v1: https://lore.kernel.org/all/20251117191815.69556-1-tsbogend@alpha.franken.de/
> 
>  arch/mips/kernel/process.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index 29191fa1801e..a3101f2268c6 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -692,7 +692,7 @@ unsigned long mips_stack_top(void)
>  	/* Space for the VDSO, data page & GIC user page */
>  	if (current->thread.abi) {
>  		top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> -		top -= PAGE_SIZE;
> +		top -= VDSO_NR_PAGES * PAGE_SIZE;
>  		top -= mips_gic_present() ? PAGE_SIZE : 0;
>  
>  		/* Space to randomize the VDSO base */
> -- 
> 2.43.0
> 

Re: [PATCH v2] MIPS: kernel: Fix random segmentation faults

[Huacai Chen]

On Thu, Nov 20, 2025 at 8:21 PM Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> On Thu, Nov 20, 2025 at 01:10:29PM +0100, Thomas Bogendoerfer wrote:
> > Commit 69896119dc9d ("MIPS: vdso: Switch to generic storage
> > implementation") switches to a generic vdso storage, which increases
> > the number of data pages from 1 to 4. But there is only one page
> > reserved, which causes segementation faults depending where the VDSO
> > area is randomized to. To fix this use the same size of reservation
> > and allocation of the VDSO data pages.
> >
> > Fixes: 69896119dc9d ("MIPS: vdso: Switch to generic storage implementation")
>
> Thanks!
>
> Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>

>
> > Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > ---
> > v2: Don't reserve additionnal VDSO_NR_PAGES, but reserve VDSO_NR_PAGES
> >     instead of the one page before.
> >     Reworked description
> > v1: https://lore.kernel.org/all/20251117191815.69556-1-tsbogend@alpha.franken.de/
> >
> >  arch/mips/kernel/process.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> > index 29191fa1801e..a3101f2268c6 100644
> > --- a/arch/mips/kernel/process.c
> > +++ b/arch/mips/kernel/process.c
> > @@ -692,7 +692,7 @@ unsigned long mips_stack_top(void)
> >       /* Space for the VDSO, data page & GIC user page */
> >       if (current->thread.abi) {
> >               top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> > -             top -= PAGE_SIZE;
> > +             top -= VDSO_NR_PAGES * PAGE_SIZE;
> >               top -= mips_gic_present() ? PAGE_SIZE : 0;
> >
> >               /* Space to randomize the VDSO base */
> > --
> > 2.43.0
> >
>

Re: [PATCH v2] MIPS: kernel: Fix random segmentation faults

[Thomas Gleixner]

On Thu, Nov 20 2025 at 13:10, Thomas Bogendoerfer wrote:
> Commit 69896119dc9d ("MIPS: vdso: Switch to generic storage
> implementation") switches to a generic vdso storage, which increases
> the number of data pages from 1 to 4. But there is only one page
> reserved, which causes segementation faults depending where the VDSO
> area is randomized to. To fix this use the same size of reservation
> and allocation of the VDSO data pages.
>
> Fixes: 69896119dc9d ("MIPS: vdso: Switch to generic storage implementation")
> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

I assume this goes through the MIPS tree to Linus.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Re: [PATCH v2] MIPS: kernel: Fix random segmentation faults

[Thomas Bogendoerfer]

On Thu, Nov 20, 2025 at 01:10:29PM +0100, Thomas Bogendoerfer wrote:
> Commit 69896119dc9d ("MIPS: vdso: Switch to generic storage
> implementation") switches to a generic vdso storage, which increases
> the number of data pages from 1 to 4. But there is only one page
> reserved, which causes segementation faults depending where the VDSO
> area is randomized to. To fix this use the same size of reservation
> and allocation of the VDSO data pages.
> 
> Fixes: 69896119dc9d ("MIPS: vdso: Switch to generic storage implementation")
> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> ---
> v2: Don't reserve additionnal VDSO_NR_PAGES, but reserve VDSO_NR_PAGES
>     instead of the one page before.
>     Reworked description
> v1: https://lore.kernel.org/all/20251117191815.69556-1-tsbogend@alpha.franken.de/
> 
>  arch/mips/kernel/process.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index 29191fa1801e..a3101f2268c6 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -692,7 +692,7 @@ unsigned long mips_stack_top(void)
>  	/* Space for the VDSO, data page & GIC user page */
>  	if (current->thread.abi) {
>  		top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> -		top -= PAGE_SIZE;
> +		top -= VDSO_NR_PAGES * PAGE_SIZE;
>  		top -= mips_gic_present() ? PAGE_SIZE : 0;
>  
>  		/* Space to randomize the VDSO base */
> -- 
> 2.43.0

applied to mips-fixes.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]