[PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

[PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

[Christophe Leroy]

As seen below, allthough the init sections have been freed, the
associated memory area is still marked as executable in the
page tables. This patch fixes that.

[    5.860093] Freeing unused kernel memory: 592K (c0570000 - c0604000)

---[ Start of kernel VM ]---
0xc0000000-0xc0497fff        4704K  rw  X  present dirty accessed shared
0xc0498000-0xc056ffff         864K  rw     present dirty accessed shared
0xc0570000-0xc059ffff         192K  rw  X  present dirty accessed shared
0xc05a0000-0xc7ffffff      125312K  rw     present dirty accessed shared
---[ vmalloc() Area ]---

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/mem.c        |  3 +++
 arch/powerpc/mm/mmu_decl.h   |  1 +
 arch/powerpc/mm/pgtable_32.c | 20 ++++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 9ee536ec0739..e95931c4e6cf 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -401,6 +401,9 @@ void free_initmem(void)
 {
 	ppc_md.progress = ppc_printk_progress;
 	free_initmem_default(POISON_FREE_INITMEM);
+#ifdef CONFIG_PPC32
+	remap_init_ram();
+#endif
 }
 
 #ifdef CONFIG_BLK_DEV_INITRD
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index f988db655e5b..d39d92600839 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -95,6 +95,7 @@ extern void _tlbia(void);
 
 extern void mapin_ram(void);
 extern int map_page(unsigned long va, phys_addr_t pa, int flags);
+void remap_init_ram(void);
 extern void setbat(int index, unsigned long virt, phys_addr_t phys,
 		   unsigned int size, pgprot_t prot);
 
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index a65c0b4c0669..d506bd61b629 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
         return(retval);
 }
 
+void remap_init_ram(void)
+{
+	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
+	unsigned long end = (unsigned long)_einittext;
+	unsigned long va;
+
+	for (va = start; va < end; va += PAGE_SIZE) {
+		pte_t *kpte;
+		pmd_t *kpmd;
+		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
+
+		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
+			continue;
+		__set_pte_at(&init_mm, va, kpte, pte, 0);
+		wmb();
+		pte_unmap(kpte);
+	}
+	flush_tlb_kernel_range(start, end);
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 
 static int __change_page_attr(struct page *page, pgprot_t prot)
-- 
2.12.0

Re: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

[Michael Ellerman]

Christophe Leroy <christophe.leroy@c-s.fr> writes:

> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 9ee536ec0739..e95931c4e6cf 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -401,6 +401,9 @@ void free_initmem(void)
>  {
>  	ppc_md.progress = ppc_printk_progress;
>  	free_initmem_default(POISON_FREE_INITMEM);
> +#ifdef CONFIG_PPC32
> +	remap_init_ram();
> +#endif
>  }

Please don't put ifdefs straight in C code like that unless you have to.
In this case it's easy to put an empty version in a header, eg:

> diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
> index f988db655e5b..d39d92600839 100644
> --- a/arch/powerpc/mm/mmu_decl.h
> +++ b/arch/powerpc/mm/mmu_decl.h
> @@ -95,6 +95,7 @@ extern void _tlbia(void);
>  
>  extern void mapin_ram(void);
>  extern int map_page(unsigned long va, phys_addr_t pa, int flags);

  +#ifdef CONFIG_PPC32
> +void remap_init_ram(void);
  +#else
  +static inline void remap_init_ram(void) { }
  +#endif

> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index a65c0b4c0669..d506bd61b629 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
>          return(retval);
>  }
>  
> +void remap_init_ram(void)
> +{
> +	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
> +	unsigned long end = (unsigned long)_einittext;
> +	unsigned long va;
> +
> +	for (va = start; va < end; va += PAGE_SIZE) {
> +		pte_t *kpte;
> +		pmd_t *kpmd;
> +		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
> +
> +		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
> +			continue;
> +		__set_pte_at(&init_mm, va, kpte, pte, 0);
> +		wmb();
> +		pte_unmap(kpte);
> +	}
> +	flush_tlb_kernel_range(start, end);
> +}

Can we just use unmap_kernel_range() ?

Is this sufficient on all 32-bit PPC? (I have no idea)

cheers

Re: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

[Christophe LEROY]

Le 18/04/2017 à 08:40, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
>
>> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
>> index a65c0b4c0669..d506bd61b629 100644
>> --- a/arch/powerpc/mm/pgtable_32.c
>> +++ b/arch/powerpc/mm/pgtable_32.c
>> @@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
>>          return(retval);
>>  }
>>
>> +void remap_init_ram(void)
>> +{
>> +	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
>> +	unsigned long end = (unsigned long)_einittext;
>> +	unsigned long va;
>> +
>> +	for (va = start; va < end; va += PAGE_SIZE) {
>> +		pte_t *kpte;
>> +		pmd_t *kpmd;
>> +		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
>> +
>> +		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
>> +			continue;
>> +		__set_pte_at(&init_mm, va, kpte, pte, 0);
>> +		wmb();
>> +		pte_unmap(kpte);
>> +	}
>> +	flush_tlb_kernel_range(start, end);
>> +}
>
> Can we just use unmap_kernel_range() ?

We only want to remove the X bit.
I think unmap_kernel_range() will unmap the area, wheareas we want to 
keep it as part of the linear data area.

Christophe

>
> Is this sufficient on all 32-bit PPC? (I have no idea)
>
> cheers
>