[PATCH 5.4 172/177] powerpc: Define arch_is_kernel_initmem_freed() for lockdep

Greg Kroah-Hartman
2019-12-16T18:21:43Z

From: Michael Ellerman <mpe@ellerman.id.au>

commit 6f07048c00fd100ed8cab66c225c157e0b6c0a50 upstream.

Under certain circumstances, we hit a warning in lockdep_register_key:

if (WARN_ON_ONCE(static_obj(key)))
return;

This occurs when the key falls into initmem that has since been freed
and can now be reused. This has been observed on boot, and under
memory pressure.

Define arch_is_kernel_initmem_freed(), which allows lockdep to
correctly identify this memory as dynamic.

This fixes a bug picked up by the powerpc64 syzkaller instance where
we hit the WARN via alloc_netdev_mqs.

Reported-by: Qian Cai <cai@lca.pw>
Reported-by: ppc syzbot c/o Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Link: https://lore.kernel.org/r/87lfs4f7d6.fsf@dja-thinkpad.axtens.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/include/asm/sections.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)

--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -5,8 +5,22 @@

#include <linux/elf.h>
#include <linux/uaccess.h>
+
+#define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
+
#include <asm-generic/sections.h>

+extern bool init_mem_is_free;
+
+static inline int arch_is_kernel_initmem_freed(unsigned long addr)
+{
+ if (!init_mem_is_free)
+ return 0;
+
+ return addr >= (unsigned long)__init_begin &&
+ addr < (unsigned long)__init_end;
+}
+
extern char __head_end[];

#ifdef __powerpc64__