linux-kernel - Re: [PATCH] Added ability to vmalloc executable memory

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Date:   Fri, 9 Dec 2022 14:51:19 +0100
From:   Xander <xandermoerkerken@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Mark Rutland <mark.rutland@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xander Moerkerken <xander.moerkerken@...on.com>
Subject: Re: [PATCH] Added ability to vmalloc executable memory

On Fri, 9 Dec 2022 at 14:46, Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> 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
>

Loud and clear, thanks for the feedback.

> >
> > On Fri, 9 Dec 2022 at 14:17, Mark Rutland <mark.rutland@....com
> > <mailto:mark.rutland@....com>> wrote:
> >
> >     On Fri, Dec 09, 2022 at 02:10:52PM +0100, Xander Moerkerken wrote:
> >      > From: Xander Moerkerken <xander.moerkerken@...il.com
> >     <mailto:xander.moerkerken@...il.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@...on.com
> >     <mailto:xander.moerkerken@...on.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
> >      >
> >