[PATCH] powerpc: Add set_memory_{p/np}() and remove set_memory_attr()

[PATCH] powerpc: Add set_memory_{p/np}() and remove set_memory_attr()

[Christophe Leroy]

set_memory_attr() was implemented by commit 4d1755b6a762 ("powerpc/mm:
implement set_memory_attr()") because the set_memory_xx() couldn't
be used at that time to modify memory "on the fly" as explained it
the commit.

But set_memory_attr() uses set_pte_at() which leads to warnings when
CONFIG_DEBUG_VM is selected, because set_pte_at() is unexpected for
updating existing page table entries.

The check could be bypassed by using __set_pte_at() instead,
as it was the case before commit c988cfd38e48 ("powerpc/32:
use set_memory_attr()") but since commit 9f7853d7609d ("powerpc/mm:
Fix set_memory_*() against concurrent accesses") it is now possible
to use set_memory_xx() functions to update page table entries
"on the fly" because the update is now atomic.

For DEBUG_PAGEALLOC we need to clear and set back _PAGE_PRESENT.
Add set_memory_np() and set_memory_p() for that.

Replace all uses of set_memory_attr() by the relevant set_memory_xx()
and remove set_memory_attr().

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()")
Cc: stable@vger.kernel.org
Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/book3s/32/pgtable.h | 10 +++++
 arch/powerpc/include/asm/book3s/64/pgtable.h | 10 +++++
 arch/powerpc/include/asm/nohash/pgtable.h    | 10 +++++
 arch/powerpc/include/asm/set_memory.h        | 12 +++++-
 arch/powerpc/mm/pageattr.c                   | 39 +++-----------------
 arch/powerpc/mm/pgtable_32.c                 | 24 ++++++------
 6 files changed, 58 insertions(+), 47 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index 609c80f67194..4ceebb291896 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
@@ -518,6 +518,16 @@ static inline pte_t pte_mkuser(pte_t pte)
 	return __pte(pte_val(pte) | _PAGE_USER);
 }
 
+static inline pte_t pte_mkpresent(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_PRESENT);
+}
+
+static inline pte_t pte_mkabsent(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~_PAGE_PRESENT);
+}
+
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	return __pte((pte_val(pte) & _PAGE_CHG_MASK) | pgprot_val(newprot));
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 33e073d6b0c4..2bbc8b69b7f4 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -724,6 +724,16 @@ static inline pte_t pte_mkuser(pte_t pte)
 	return __pte_raw(pte_raw(pte) & cpu_to_be64(~_PAGE_PRIVILEGED));
 }
 
+static inline pte_t pte_mkpresent(pte_t pte)
+{
+	return __pte_raw(pte_raw(pte) | cpu_to_be64(_PAGE_PRESENT));
+}
+
+static inline pte_t pte_mkabsent(pte_t pte)
+{
+	return __pte_raw(pte_raw(pte) & cpu_to_be64(~_PAGE_PRESENT));
+}
+
 /*
  * This is potentially called with a pmd as the argument, in which case it's not
  * safe to check _PAGE_DEVMAP unless we also confirm that _PAGE_PTE is set.
diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
index ac75f4ab0dba..3d4169969900 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h
@@ -166,6 +166,16 @@ static inline pte_t pte_mkuser(pte_t pte)
 }
 #endif
 
+static inline pte_t pte_mkpresent(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_PRESENT);
+}
+
+static inline pte_t pte_mkabsent(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~_PAGE_PRESENT);
+}
+
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	return __pte((pte_val(pte) & _PAGE_CHG_MASK) | pgprot_val(newprot));
diff --git a/arch/powerpc/include/asm/set_memory.h b/arch/powerpc/include/asm/set_memory.h
index b040094f7920..061f1766a8a4 100644
--- a/arch/powerpc/include/asm/set_memory.h
+++ b/arch/powerpc/include/asm/set_memory.h
@@ -6,6 +6,8 @@
 #define SET_MEMORY_RW	1
 #define SET_MEMORY_NX	2
 #define SET_MEMORY_X	3
+#define SET_MEMORY_NP	4
+#define SET_MEMORY_P	5
 
 int change_memory_attr(unsigned long addr, int numpages, long action);
 
@@ -29,6 +31,14 @@ static inline int set_memory_x(unsigned long addr, int numpages)
 	return change_memory_attr(addr, numpages, SET_MEMORY_X);
 }
 
-int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot);
+static inline int set_memory_np(unsigned long addr, int numpages)
+{
+	return change_memory_attr(addr, numpages, SET_MEMORY_NP);
+}
+
+static inline int set_memory_p(unsigned long addr, int numpages)
+{
+	return change_memory_attr(addr, numpages, SET_MEMORY_P);
+}
 
 #endif
diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c
index edea388e9d3f..cb36963644c9 100644
--- a/arch/powerpc/mm/pageattr.c
+++ b/arch/powerpc/mm/pageattr.c
@@ -48,6 +48,12 @@ static int change_page_attr(pte_t *ptep, unsigned long addr, void *data)
 	case SET_MEMORY_X:
 		pte = pte_mkexec(pte);
 		break;
+	case SET_MEMORY_NP:
+		pte = pte_mkabsent(pte);
+		break;
+	case SET_MEMORY_P:
+		pte = pte_mkpresent(pte);
+		break;
 	default:
 		WARN_ON_ONCE(1);
 		break;
@@ -96,36 +102,3 @@ int change_memory_attr(unsigned long addr, int numpages, long action)
 	return apply_to_existing_page_range(&init_mm, start, size,
 					    change_page_attr, (void *)action);
 }
-
-/*
- * Set the attributes of a page:
- *
- * This function is used by PPC32 at the end of init to set final kernel memory
- * protection. It includes changing the maping of the page it is executing from
- * and data pages it is using.
- */
-static int set_page_attr(pte_t *ptep, unsigned long addr, void *data)
-{
-	pgprot_t prot = __pgprot((unsigned long)data);
-
-	spin_lock(&init_mm.page_table_lock);
-
-	set_pte_at(&init_mm, addr, ptep, pte_modify(*ptep, prot));
-	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
-
-	spin_unlock(&init_mm.page_table_lock);
-
-	return 0;
-}
-
-int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot)
-{
-	unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE);
-	unsigned long sz = numpages * PAGE_SIZE;
-
-	if (numpages <= 0)
-		return 0;
-
-	return apply_to_existing_page_range(&init_mm, start, sz, set_page_attr,
-					    (void *)pgprot_val(prot));
-}
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 906e4e4328b2..f71ededdc02a 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -135,10 +135,12 @@ void mark_initmem_nx(void)
 	unsigned long numpages = PFN_UP((unsigned long)_einittext) -
 				 PFN_DOWN((unsigned long)_sinittext);
 
-	if (v_block_mapped((unsigned long)_sinittext))
+	if (v_block_mapped((unsigned long)_sinittext)) {
 		mmu_mark_initmem_nx();
-	else
-		set_memory_attr((unsigned long)_sinittext, numpages, PAGE_KERNEL);
+	} else {
+		set_memory_nx((unsigned long)_sinittext, numpages);
+		set_memory_rw((unsigned long)_sinittext, numpages);
+	}
 }
 
 #ifdef CONFIG_STRICT_KERNEL_RWX
@@ -152,18 +154,14 @@ void mark_rodata_ro(void)
 		return;
 	}
 
-	numpages = PFN_UP((unsigned long)_etext) -
-		   PFN_DOWN((unsigned long)_stext);
-
-	set_memory_attr((unsigned long)_stext, numpages, PAGE_KERNEL_ROX);
 	/*
-	 * mark .rodata as read only. Use __init_begin rather than __end_rodata
-	 * to cover NOTES and EXCEPTION_TABLE.
+	 * mark .text and .rodata as read only. Use __init_begin rather than
+	 * __end_rodata to cover NOTES and EXCEPTION_TABLE.
 	 */
 	numpages = PFN_UP((unsigned long)__init_begin) -
-		   PFN_DOWN((unsigned long)__start_rodata);
+		   PFN_DOWN((unsigned long)_stext);
 
-	set_memory_attr((unsigned long)__start_rodata, numpages, PAGE_KERNEL_RO);
+	set_memory_ro((unsigned long)_stext, numpages);
 
 	// mark_initmem_nx() should have already run by now
 	ptdump_check_wx();
@@ -179,8 +177,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 		return;
 
 	if (enable)
-		set_memory_attr(addr, numpages, PAGE_KERNEL);
+		set_memory_p(addr, numpages);
 	else
-		set_memory_attr(addr, numpages, __pgprot(0));
+		set_memory_np(addr, numpages);
 }
 #endif /* CONFIG_DEBUG_PAGEALLOC */
-- 
2.33.1

Re: [PATCH] powerpc: Add set_memory_{p/np}() and remove set_memory_attr()

[Maxime Bizon]

On Friday 10 Dec 2021 à 08:09:42 (+0000), Christophe Leroy wrote:

Tested-by: Maxime Bizon <mbizon@freebox.fr>

-- 
Maxime

Re: [PATCH] powerpc: Add set_memory_{p/np}() and remove set_memory_attr()

[Russell Currey]

On Fri, 2021-12-10 at 08:09 +0000, Christophe Leroy wrote:
> set_memory_attr() was implemented by commit 4d1755b6a762
> ("powerpc/mm:
> implement set_memory_attr()") because the set_memory_xx() couldn't
> be used at that time to modify memory "on the fly" as explained it
> the commit.
> 
> But set_memory_attr() uses set_pte_at() which leads to warnings when
> CONFIG_DEBUG_VM is selected, because set_pte_at() is unexpected for
> updating existing page table entries.
> 
> The check could be bypassed by using __set_pte_at() instead,
> as it was the case before commit c988cfd38e48 ("powerpc/32:
> use set_memory_attr()") but since commit 9f7853d7609d ("powerpc/mm:
> Fix set_memory_*() against concurrent accesses") it is now possible
> to use set_memory_xx() functions to update page table entries
> "on the fly" because the update is now atomic.
> 
> For DEBUG_PAGEALLOC we need to clear and set back _PAGE_PRESENT.
> Add set_memory_np() and set_memory_p() for that.
> 
> Replace all uses of set_memory_attr() by the relevant set_memory_xx()
> and remove set_memory_attr().
> 
> Reported-by: Maxime Bizon <mbizon@freebox.fr>
> Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()")
> Cc: stable@vger.kernel.org
> Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against
> concurrent accesses")
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

Reviewed-by: Russell Currey <ruscur@russell.cc>

One comment below:

> diff --git a/arch/powerpc/include/asm/set_memory.h
> b/arch/powerpc/include/asm/set_memory.h
> index b040094f7920..061f1766a8a4 100644
> --- a/arch/powerpc/include/asm/set_memory.h
> +++ b/arch/powerpc/include/asm/set_memory.h
> @@ -6,6 +6,8 @@
>  #define SET_MEMORY_RW  1
>  #define SET_MEMORY_NX  2
>  #define SET_MEMORY_X   3
> +#define SET_MEMORY_NP  4
> +#define SET_MEMORY_P   5

It might be nice to have a comment somewhere in set_memory.h explaining
that {p/np} = present/not present.  RO/RW/NX/X are commonly used, "p"
as shorthand for "present" is less obvious.  x86's set_memory.h has a
nice comment covering everything as an example.

>  int change_memory_attr(unsigned long addr, int numpages, long
> action);
>  
> @@ -29,6 +31,14 @@ static inline int set_memory_x(unsigned long addr,
> int numpages)
>         return change_memory_attr(addr, numpages, SET_MEMORY_X);
>  }
>  
> -int set_memory_attr(unsigned long addr, int numpages, pgprot_t
> prot);
> +static inline int set_memory_np(unsigned long addr, int numpages)
> +{
> +       return change_memory_attr(addr, numpages, SET_MEMORY_NP);
> +}
> +
> +static inline int set_memory_p(unsigned long addr, int numpages)
> +{
> +       return change_memory_attr(addr, numpages, SET_MEMORY_P);
> +}
>  
>  #endif