[PATCH v2] ARM: mm: fix size rounding-down of arm_add_memory() function

The current rounding of "size" is wrong:

 - If "start" is sufficiently near the next page boundary, "size"
   is decremented by more than enough and the last page is lost.

 - If "size" is sufficiently small, it is wrapped around and gets
   a bogus value.

Signed-off-by: Masahiro Yamada <redacted>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
---

Changes in v2:
 - Avoid wrap around of "size"

 arch/arm/kernel/setup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f9c8639..d13f185 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c

@@ -657,10 +657,13 @@ int __init arm_add_memory(u64 start, u64 size)
 
 	/*
 	 * Ensure that start/size are aligned to a page boundary.
-	 * Size is appropriately rounded down, start is rounded up.
+	 * Size is rounded down, start is rounded up.
 	 */
-	size -= start & ~PAGE_MASK;
 	aligned_start = PAGE_ALIGN(start);
+	if (aligned_start > start + size)
+		size = 0;
+	else
+		size -= aligned_start - start;
 
 #ifndef CONFIG_ARCH_PHYS_ADDR_T_64BIT
 	if (aligned_start > ULONG_MAX) {

-- 
1.9.1

On 22 December 2014 at 04:17, Masahiro Yamada [off-list ref] wrote:

The current rounding of "size" is wrong:

 - If "start" is sufficiently near the next page boundary, "size"
   is decremented by more than enough and the last page is lost.

 - If "size" is sufficiently small, it is wrapped around and gets
   a bogus value.

Signed-off-by: Masahiro Yamada <redacted>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Acked-by: Ard Biesheuvel <redacted>

Hello Russell King,

Could you apply this patch for arm_add_memory() fix, please ?


Thanks,
Masahiro Yamada


On Mon, 22 Dec 2014 10:09:32 +0100
Ard Biesheuvel [off-list ref] wrote:

On 22 December 2014 at 04:17, Masahiro Yamada [off-list ref] wrote:

quoted

The current rounding of "size" is wrong:

 - If "start" is sufficiently near the next page boundary, "size"
   is decremented by more than enough and the last page is lost.

 - If "size" is sufficiently small, it is wrapped around and gets
   a bogus value.

Signed-off-by: Masahiro Yamada <redacted>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Acked-by: Ard Biesheuvel <redacted>

quoted

---

Changes in v2:
 - Avoid wrap around of "size"

 arch/arm/kernel/setup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f9c8639..d13f185 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c

@@ -657,10 +657,13 @@ int __init arm_add_memory(u64 start, u64 size)

        /*
         * Ensure that start/size are aligned to a page boundary.
-        * Size is appropriately rounded down, start is rounded up.
+        * Size is rounded down, start is rounded up.
         */
-       size -= start & ~PAGE_MASK;
        aligned_start = PAGE_ALIGN(start);
+       if (aligned_start > start + size)
+               size = 0;
+       else
+               size -= aligned_start - start;

 #ifndef CONFIG_ARCH_PHYS_ADDR_T_64BIT
        if (aligned_start > ULONG_MAX) {
--

1.9.1

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