Re: [PATCH 07/32] mm: Bring back vmalloc_exec

[Christophe Leroy]

Le 09/05/2023 à 18:56, Kent Overstreet a écrit :
> From: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> 
> This is needed for bcachefs, which dynamically generates per-btree node
> unpack functions.
> 
> Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> ---
>   include/linux/vmalloc.h |  1 +
>   kernel/module/main.c    |  4 +---
>   mm/nommu.c              | 18 ++++++++++++++++++
>   mm/vmalloc.c            | 21 +++++++++++++++++++++
>   4 files changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 69250efa03..ff147fe115 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -145,6 +145,7 @@ extern void *vzalloc(unsigned long size) __alloc_size(1);
>   extern void *vmalloc_user(unsigned long size) __alloc_size(1);
>   extern void *vmalloc_node(unsigned long size, int node) __alloc_size(1);
>   extern void *vzalloc_node(unsigned long size, int node) __alloc_size(1);
> +extern void *vmalloc_exec(unsigned long size, gfp_t gfp_mask) __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);
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index d3be89de70..9eaa89e84c 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1607,9 +1607,7 @@ static void dynamic_debug_remove(struct module *mod, struct _ddebug_info *dyndbg
>   
>   void * __weak module_alloc(unsigned long size)
>   {
> -	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
> -			GFP_KERNEL, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS,
> -			NUMA_NO_NODE, __builtin_return_address(0));
> +	return vmalloc_exec(size, GFP_KERNEL);
>   }
>   
>   bool __weak module_init_section(const char *name)
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 57ba243c6a..8d9ab19e39 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -280,6 +280,24 @@ void *vzalloc_node(unsigned long size, int node)
>   }
>   EXPORT_SYMBOL(vzalloc_node);
>   
> +/**
> + *	vmalloc_exec  -  allocate virtually contiguous, executable memory
> + *	@size:		allocation size
> + *
> + *	Kernel-internal function to allocate enough pages to cover @size
> + *	the page level allocator and map them into contiguous and
> + *	executable kernel virtual space.
> + *
> + *	For tight control over page level allocator and protection flags
> + *	use __vmalloc() instead.
> + */
> +
> +void *vmalloc_exec(unsigned long size, gfp_t gfp_mask)
> +{
> +	return __vmalloc(size, gfp_mask);
> +}
> +EXPORT_SYMBOL_GPL(vmalloc_exec);
> +
>   /**
>    * vmalloc_32  -  allocate virtually contiguous memory (32bit addressable)
>    *	@size:		allocation size
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 31ff782d36..2ebb9ea7f0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3401,6 +3401,27 @@ void *vzalloc_node(unsigned long size, int node)
>   }
>   EXPORT_SYMBOL(vzalloc_node);
>   
> +/**
> + * vmalloc_exec - allocate virtually contiguous, executable memory
> + * @size:	  allocation size
> + *
> + * Kernel-internal function to allocate enough pages to cover @size
> + * the page level allocator and map them into contiguous and
> + * executable kernel virtual space.
> + *
> + * For tight control over page level allocator and protection flags
> + * use __vmalloc() instead.
> + *
> + * Return: pointer to the allocated memory or %NULL on error
> + */
> +void *vmalloc_exec(unsigned long size, gfp_t gfp_mask)
> +{
> +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
> +			gfp_mask, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS,
> +			NUMA_NO_NODE, __builtin_return_address(0));
> +}

That cannot work. The VMALLOC space is mapped non-exec on powerpc/32. 
You have to allocate between MODULES_VADDR and MODULES_END if you want 
something executable so you must use module_alloc() see 
https://elixir.bootlin.com/linux/v6.4-rc1/source/arch/powerpc/kernel/module.c#L108

> +EXPORT_SYMBOL_GPL(vmalloc_exec);
> +
>   #if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32)
>   #define GFP_VMALLOC32 (GFP_DMA32 | GFP_KERNEL)
>   #elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA)