Re: [PATCH] Added ability to vmalloc executable memory

Christophe Leroy
2022-12-09T13:46:19Z

Le 09/12/2022 à 14:38, Xander a écrit :
>
> The pgprot parameter got removed because, according to the commit log,
> for no other apparent reason than it being called with 'PAGE_KERNEL' as
> an argument in the whole kernel. Therefore it got removed.
> This removed the ability to allocate virtual memory with executing rights.
> My use case comes from ioremap().
> I think this is useful for others too.
>
> I don't see why this pgprot parameter got removed but this is the
> alternative to reverting it to the older 5.7 function.

Please avoid top-posting, and use only plain text.

I think you don't answer to Mark's question.

You are adding a new function that no driver uses apparently. If you are
working on some piece of code that needs this new fonction, you can send
this patch as part of a patch series including that code.

By the way, when you need executable memory, the fonction to use is
module_alloc(), that's the only function that garanties real executable
memory on all platforms. For instance, on some powerpc, setting the X
bit is not enough to get executable memory in vmalloc space.

Christophe

>
> On Fri, 9 Dec 2022 at 14:17, Mark Rutland <mark.rutland@arm.com
> <mailto:mark.rutland@arm.com>> wrote:
>
> On Fri, Dec 09, 2022 at 02:10:52PM +0100, Xander Moerkerken wrote:
> > From: Xander Moerkerken <xander.moerkerken@gmail.com
> <mailto:xander.moerkerken@gmail.com>>
> >
> > Since release 5.8-rc1 the pgprot got removed from __vmalloc
> > because the only usage was PAGE_KERNEL as argument.
> > However, this removes the ability to input other arguments
> > such as 'PAGE_KERNEL_EXEC', which can be used to allocate
> > memory in which you can execute. For this reason a new
> > function is introduced called '__vmalloc_exec'.
> >
> > Signed-off-by: Xander Moerkerken <xander.moerkerken@omron.com
> <mailto:xander.moerkerken@omron.com>>
>
> What is this going to be used for? There's no user from this patch
> alone, as a
> module or otherwise.
>
> Mark.
>
> > ---
> >  include/linux/vmalloc.h | 1 +
> >  mm/vmalloc.c            | 8 ++++++++
> >  2 files changed, 9 insertions(+)
> >
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index 096d48aa3437..10c46513b6b2 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -147,6 +147,7 @@ extern void *vzalloc_node(unsigned long size,
> int node) __alloc_size(1);
> >  extern void *vmalloc_32(unsigned long size) __alloc_size(1);
> >  extern void *vmalloc_32_user(unsigned long size) __alloc_size(1);
> >  extern void *__vmalloc(unsigned long size, gfp_t gfp_mask)
> __alloc_size(1);
> > +extern void *__vmalloc_exec(unsigned long size, gfp_t gfp_mask)
> __alloc_size(1);
> >  extern void *__vmalloc_node_range(unsigned long size, unsigned
> long align,
> >                       unsigned long start, unsigned long end,
> gfp_t gfp_mask,
> >                       pgprot_t prot, unsigned long vm_flags, int
> node,
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index ccaa461998f3..8fd01ed7082b 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3294,6 +3294,14 @@ void *__vmalloc(unsigned long size, gfp_t
> gfp_mask)
> >  }
> >  EXPORT_SYMBOL(__vmalloc);
> >
> > +
> > +void *__vmalloc_exec(unsigned long size, gfp_t gfp_mask)
> > +{
> > +     return __vmalloc_node_prot(size, 1, gfp_mask, PAGE_KERNEL_EXEC,
> > +                               NUMA_NO_NODE,
> __builtin_return_address(0));
> > +}
> > +EXPORT_SYMBOL(__vmalloc_exec);
> > +
> >  /**
> >   * vmalloc - allocate virtually contiguous memory
> >   * @size:    allocation size
> > --
> > 2.37.2
> >
>