1. Do not use memcmp() on unallocated memory, as the new introduced
fortify dynamic object size check[1] will return unexpected result.
2. Use a fixed pattern instead of a random function pointer as the
magic value. "0xaa5555aa" has a large information entropy and is
widely used in memory testing.
3. Flip the magic value and double check it to ensure memory overlap.
Tested on ralink/mt7620 and ath79/ar9344
[1] commit 439a1bcac648 ("fortify: Use __builtin_dynamic_object_size() when available")
Signed-off-by: Shiji Yang <yangshiji66@xxxxxxxxxxx>
Tested-by: Mieczyslaw Nalewaj <namiltd@xxxxxxxxx>
---
changes:
v2 -> v3:
* Using CKSEG1ADDR_OR_64BIT() instead of excluding 64bit system.
* Using volatile pointer to get and compare u32 data.
v1:
https://lore.kernel.org/all/TYAP286MB0315E609C476B86E22700626BC292@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
v2:
https://lore.kernel.org/all/TYCP286MB089598ABD1E2F66003D71EB8BCD52@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
arch/mips/kernel/setup.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 12a1a4ffb602..4197c7568f49 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -86,21 +86,26 @@ static struct resource bss_resource = { .name = "Kernel bss", };
unsigned long __kaslr_offset __ro_after_init;
EXPORT_SYMBOL(__kaslr_offset);
-static void *detect_magic __initdata = detect_memory_region;
-
#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
unsigned long ARCH_PFN_OFFSET;
EXPORT_SYMBOL(ARCH_PFN_OFFSET);
#endif
+#define MIPS_MEM_TEST_PATTERN 0xaa5555aa
+
void __init detect_memory_region(phys_addr_t start, phys_addr_t sz_min, phys_addr_t sz_max)
{
- void *dm = &detect_magic;
+ u32 detect_magic;
+ volatile u32 *dm = (volatile u32 *)CKSEG1ADDR_OR_64BIT(&detect_magic);
phys_addr_t size;
for (size = sz_min; size < sz_max; size <<= 1) {
- if (!memcmp(dm, dm + size, sizeof(detect_magic)))
- break;
+ *dm = MIPS_MEM_TEST_PATTERN;
+ if (*dm == *(volatile u32 *)((void *)dm + size)) {
+ *dm = ~MIPS_MEM_TEST_PATTERN;
+ if (*dm == *(volatile u32 *)((void *)dm + size))
+ break;
+ }
}
pr_debug("Memory: %lluMB of RAM detected at 0x%llx (min: %lluMB, max: %lluMB)\n",
--
2.45.1
