Re: [PATCH v11 00/11] Support page table check PowerPC

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 28/03/2024 à 08:57, Christophe Leroy a écrit :
> 
> 
> Le 28/03/2024 à 07:52, Christophe Leroy a écrit :
>>
>>
>> Le 28/03/2024 à 05:55, Rohan McLure a écrit :
>>> Support page table check on all PowerPC platforms. This works by
>>> serialising assignments, reassignments and clears of page table
>>> entries at each level in order to ensure that anonymous mappings
>>> have at most one writable consumer, and likewise that file-backed
>>> mappings are not simultaneously also anonymous mappings.
>>>
>>> In order to support this infrastructure, a number of stubs must be
>>> defined for all powerpc platforms. Additionally, seperate set_pte_at()
>>> and set_pte_at_unchecked(), to allow for internal, uninstrumented 
>>> mappings.
>>
>> I gave it a try on QEMU e500 (64 bits), and get the following Oops. 
>> What do I have to look for ?
>>
>> Freeing unused kernel image (initmem) memory: 2588K
>> This architecture does not have kernel memory protection.
>> Run /init as init process
>> ------------[ cut here ]------------
>> kernel BUG at mm/page_table_check.c:119!
>> Oops: Exception in kernel mode, sig: 5 [#1]
>> BE PAGE_SIZE=4K SMP NR_CPUS=32 QEMU e500
> 
> Same problem on my 8xx board:
> 
> [    7.358146] Freeing unused kernel image (initmem) memory: 448K
> [    7.363957] Run /init as init process
> [    7.370955] ------------[ cut here ]------------
> [    7.375411] kernel BUG at mm/page_table_check.c:119!
> [    7.380393] Oops: Exception in kernel mode, sig: 5 [#1]
> [    7.385621] BE PAGE_SIZE=16K PREEMPT CMPC885

Both problems are fixed by following change:

diff --git a/arch/powerpc/include/asm/nohash/pgtable.h 
b/arch/powerpc/include/asm/nohash/pgtable.h
index 413d01a51e6f..5b932632a5d7 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h
@@ -29,6 +29,8 @@ static inline pte_basic_t pte_update(struct mm_struct 
*mm, unsigned long addr, p

  #ifndef __ASSEMBLY__

+#include <linux/page_table_check.h>
+
  extern int icache_44x_need_flush;

  /*
@@ -92,7 +94,11 @@ static inline void ptep_set_wrprotect(struct 
mm_struct *mm, unsigned long addr,
  static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned 
long addr,
  				       pte_t *ptep)
  {
-	return __pte(pte_update(mm, addr, ptep, ~0UL, 0, 0));
+	pte_t old_pte = __pte(pte_update(mm, addr, ptep, ~0UL, 0, 0));
+
+	page_table_check_pte_clear(mm, addr, old_pte);
+
+	return old_pte;
  }
  #define __HAVE_ARCH_PTEP_GET_AND_CLEAR