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

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Message-ID: <ed1c32c0-e882-e7f8-3acf-0c0204fb96ae@csgroup.eu>
Date:   Fri, 9 Dec 2022 13:46:05 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Xander <xandermoerkerken@...il.com>,
        Mark Rutland <mark.rutland@....com>
CC:     "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



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@....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
>      >
>