Re: [PATCH 3/3] mm/vmalloc: Sync unmappings in vunmap_page_range()

[Joerg Roedel]

Srewed up the subject :(, it needs to be

	"mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()"

of course.

On Fri, Jul 19, 2019 at 08:46:52PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@xxxxxxx>
> 
> On x86-32 with PTI enabled, parts of the kernel page-tables
> are not shared between processes. This can cause mappings in
> the vmalloc/ioremap area to persist in some page-tables
> after the region is unmapped and released.
> 
> When the region is re-used the processes with the old
> mappings do not fault in the new mappings but still access
> the old ones.
> 
> This causes undefined behavior, in reality often data
> corruption, kernel oopses and panics and even spontaneous
> reboots.
> 
> Fix this problem by activly syncing unmaps in the
> vmalloc/ioremap area to all page-tables in the system before
> the regions can be re-used.
> 
> References: https://bugzilla.suse.com/show_bug.cgi?id=1118689
> Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Fixes: 5d72b4fba40ef ('x86, mm: support huge I/O mapping capability I/F')
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
>  mm/vmalloc.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 4fa8d84599b0..e0fc963acc41 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1258,6 +1258,12 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
>  	if (unlikely(valist == NULL))
>  		return false;
>  
> +	/*
> +	 * First make sure the mappings are removed from all page-tables
> +	 * before they are freed.
> +	 */
> +	vmalloc_sync_all();
> +
>  	/*
>  	 * TODO: to calculate a flush range without looping.
>  	 * The list can be up to lazy_max_pages() elements.
> @@ -3038,6 +3044,9 @@ EXPORT_SYMBOL(remap_vmalloc_range);
>  /*
>   * Implement a stub for vmalloc_sync_all() if the architecture chose not to
>   * have one.
> + *
> + * The purpose of this function is to make sure the vmalloc area
> + * mappings are identical in all page-tables in the system.
>   */
>  void __weak vmalloc_sync_all(void)
>  {
> -- 
> 2.17.1