Re: [PATCH] x86/kasan: map shadow for percpu pages on demand

["Yin, Fengwei" <fengwei.yin@intel.com>]

Hi Andrey,

On 10/28/2022 5:31 AM, Andrey Ryabinin wrote:
> KASAN maps shadow for the entire CPU-entry-area:
>   [CPU_ENTRY_AREA_BASE, CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE]
> 
> This explodes after commit 1248fb6a8201 ("x86/mm: Randomize per-cpu entry area")
> since it increases CPU_ENTRY_AREA_MAP_SIZE to 512 GB and KASAN fails
> to allocate shadow for such big area.
> 
> Fix this by allocating KASAN shadow only for really used cpu entry area
> addresses mapped by cea_map_percpu_pages()
> 
> Fixes: 1248fb6a8201 ("x86/mm: Randomize per-cpu entry area")
> Reported-by: kernel test robot <yujie.liu@intel.com>
> Link: https://lore.kernel.org/r/202210241508.2e203c3d-yujie.liu@intel.com
> Tested-by: Yujie Liu <yujie.liu@intel.com>
> Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> ---
>  arch/x86/include/asm/kasan.h |  3 +++
>  arch/x86/mm/cpu_entry_area.c |  8 +++++++-
>  arch/x86/mm/kasan_init_64.c  | 15 ++++++++++++---
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
> index 13e70da38bed..de75306b932e 100644
> --- a/arch/x86/include/asm/kasan.h
> +++ b/arch/x86/include/asm/kasan.h
> @@ -28,9 +28,12 @@
>  #ifdef CONFIG_KASAN
>  void __init kasan_early_init(void);
>  void __init kasan_init(void);
> +void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid);
>  #else
>  static inline void kasan_early_init(void) { }
>  static inline void kasan_init(void) { }
> +static inline void kasan_populate_shadow_for_vaddr(void *va, size_t size,
> +						   int nid) { }
>  #endif
>  
>  #endif
> diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
> index ad1f750517a1..ac2e952186c3 100644
> --- a/arch/x86/mm/cpu_entry_area.c
> +++ b/arch/x86/mm/cpu_entry_area.c
> @@ -9,6 +9,7 @@
>  #include <asm/cpu_entry_area.h>
>  #include <asm/fixmap.h>
>  #include <asm/desc.h>
> +#include <asm/kasan.h>
>  
>  static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);
>  
> @@ -91,8 +92,13 @@ void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
>  static void __init
>  cea_map_percpu_pages(void *cea_vaddr, void *ptr, int pages, pgprot_t prot)
>  {
> +	phys_addr_t pa = per_cpu_ptr_to_phys(ptr);
> +
> +	kasan_populate_shadow_for_vaddr(cea_vaddr, pages * PAGE_SIZE,
> +					early_pfn_to_nid(PFN_DOWN(pa)));
> +
>  	for ( ; pages; pages--, cea_vaddr+= PAGE_SIZE, ptr += PAGE_SIZE)
> -		cea_set_pte(cea_vaddr, per_cpu_ptr_to_phys(ptr), prot);
> +		cea_set_pte(cea_vaddr, pa, prot);
>  }
>  
>  static void __init percpu_setup_debug_store(unsigned int cpu)
> diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
> index e7b9b464a82f..d1416926ad52 100644
> --- a/arch/x86/mm/kasan_init_64.c
> +++ b/arch/x86/mm/kasan_init_64.c
> @@ -316,6 +316,18 @@ void __init kasan_early_init(void)
>  	kasan_map_early_shadow(init_top_pgt);
>  }
>  
> +void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid)
> +{
> +	unsigned long shadow_start, shadow_end;
> +
> +	shadow_start = (unsigned long)kasan_mem_to_shadow(va);
> +	shadow_start = round_down(shadow_start, PAGE_SIZE);
> +	shadow_end = (unsigned long)kasan_mem_to_shadow(va + size);
> +	shadow_end = round_up(shadow_end, PAGE_SIZE);
> +
> +	kasan_populate_shadow(shadow_start, shadow_end, nid);
> +}
> +
>  void __init kasan_init(void)
>  {
>  	int i;
> @@ -393,9 +405,6 @@ void __init kasan_init(void)
>  		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
>  		shadow_cpu_entry_begin);
>  
> -	kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
> -			      (unsigned long)shadow_cpu_entry_end, 0);
> -
There will be address in the range (shadow_cpu_entry_begin, shadow_cpu_entry_end)
which has no KASAN shadow mapping populated after the patch. Not sure whether
it could be a problem. Thanks.

Regards
Yin, Fengwei

>  	kasan_populate_early_shadow(shadow_cpu_entry_end,
>  			kasan_mem_to_shadow((void *)__START_KERNEL_map));
>