From 51c3c62b58b357e8d35e4cc32f7b4ec907426fe3 Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Fri, 14 Sep 2018 11:14:11 +1000 Subject: powerpc: Avoid code patching freed init sections This stops us from doing code patching in init sections after they've been freed. In this chain: kvm_guest_init() -> kvm_use_magic_page() -> fault_in_pages_readable() -> __get_user() -> __get_user_nocheck() -> barrier_nospec(); We have a code patching location at barrier_nospec() and kvm_guest_init() is an init function. This whole chain gets inlined, so when we free the init section (hence kvm_guest_init()), this code goes away and hence should no longer be patched. We seen this as userspace memory corruption when using a memory checker while doing partition migration testing on powervm (this starts the code patching post migration via /sys/kernel/mobility/migration). In theory, it could also happen when using /sys/kernel/debug/powerpc/barrier_nospec. Cc: stable@vger.kernel.org # 4.13+ Signed-off-by: Michael Neuling Reviewed-by: Nicholas Piggin Reviewed-by: Christophe Leroy Signed-off-by: Michael Ellerman --- arch/powerpc/lib/code-patching.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/powerpc/lib') diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index 850f3b8f4da5..6ae2777c220d 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -28,6 +28,12 @@ static int __patch_instruction(unsigned int *exec_addr, unsigned int instr, { int err; + /* Make sure we aren't patching a freed init section */ + if (init_mem_is_free && init_section_contains(exec_addr, 4)) { + pr_debug("Skipping init section patching addr: 0x%px\n", exec_addr); + return 0; + } + __put_user_size(instr, patch_addr, 4, err); if (err) return err; -- cgit v1.2.3