While reviewing a RISC-V patch cloning the Arm code, I noticed an
off-by-1 here: FIX_PMAP_{BEGIN,END} being an inclusive range and
FIX_LAST being the same as FIX_PMAP_END, FIXADDR_TOP cannot derive from
FIX_LAST alone, or else the BUG_ON() in virt_to_fix() would trigger if
FIX_PMAP_END ended up being used.
While touching this area also add a check for fixmap and boot FDT area
to not only not overlap, but to have at least one (unmapped) page in
between.
Fixes: 4f17357b52f6 ("xen/arm: add Persistent Map (PMAP) infrastructure")
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
v2: Adjust FIXADDR_TOP instead. Add BUILD_BUG_ON() as suggested by
Michal.
--- a/xen/arch/arm/include/asm/fixmap.h
+++ b/xen/arch/arm/include/asm/fixmap.h
@@ -18,7 +18,7 @@
#define FIX_LAST FIX_PMAP_END
#define FIXADDR_START FIXMAP_ADDR(0)
-#define FIXADDR_TOP FIXMAP_ADDR(FIX_LAST)
+#define FIXADDR_TOP FIXMAP_ADDR(FIX_LAST + 1)
#ifndef __ASSEMBLY__
--- a/xen/arch/arm/mmu/setup.c
+++ b/xen/arch/arm/mmu/setup.c
@@ -128,6 +128,12 @@ static void __init __maybe_unused build_
#undef CHECK_SAME_SLOT
#undef CHECK_DIFFERENT_SLOT
+
+ /*
+ * Fixmaps must not overlap with boot FDT mapping area. Make sure there's
+ * at least one guard page in between.
+ */
+ BUILD_BUG_ON(FIXADDR_TOP >= BOOT_FDT_VIRT_START);
}
lpae_t __init pte_of_xenaddr(vaddr_t va)
