linux-kernel - [PATCH 5.4 172/177] powerpc: Define arch_is_kernel_initmem

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Message-Id: <20191216174850.685064994@linuxfoundation.org>
Date:   Mon, 16 Dec 2019 18:50:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Qian Cai <cai@....pw>,
        ppc syzbot c/o Andrew Donnellan <ajd@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Daniel Axtens <dja@...ens.net>
Subject: [PATCH 5.4 172/177] powerpc: Define arch_is_kernel_initmem_freed() for lockdep

From: Michael Ellerman <mpe@...erman.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@....pw>
Reported-by: ppc syzbot c/o Andrew Donnellan <ajd@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Daniel Axtens <dja@...ens.net>
Link: https://lore.kernel.org/r/87lfs4f7d6.fsf@dja-thinkpad.axtens.net
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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__