of: check for size < 0 after rounding in early_init_dt_add_memory_arch

Memory regions passed to early_init_dt_add_memory_arch() are rounded to
PAGE_SIZE by subtracting the size of the leading fractional page from
the 'size' argument. However, size being a u64 type, if its value is
sufficiently small, the subtraction wraps around and produces a bogus
value, potentially leading to crashes.

Fix this by ignoring the memory range in such cases.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Grant Likely <grant.likely@linaro.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 535124670257..83a8e1154602 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -928,6 +928,11 @@ void __init __weak early_init_dt_add_memory_arch(u64 base, u64 size)
         const u64 phys_offset = __pa(PAGE_OFFSET);
 
         if (!PAGE_ALIGNED(base)) {
+                if (size < PAGE_SIZE - (base & ~PAGE_MASK)) {
+                        pr_warn("Ignoring memory block 0x%llx - 0x%llx\n",
+                                base, base + size);
+                        return;
+                }
                 size -= PAGE_SIZE - (base & ~PAGE_MASK);
                 base = PAGE_ALIGN(base);
         }