4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Michael Neuling <mi...@neuling.org>
commit 51c3c62b58b357e8d35e4cc32f7b4ec907426fe3 upstream.
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: sta...@vger.kernel.org # 4.13+
Signed-off-by: Michael Neuling <mi...@neuling.org>
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/powerpc/include/asm/setup.h | 1 +
arch/powerpc/lib/code-patching.c | 6 ++++++
arch/powerpc/mm/mem.c | 2 ++
3 files changed, 9 insertions(+)
--- a/arch/powerpc/include/asm/setup.h
+++ b/arch/powerpc/include/asm/setup.h
@@ -9,6 +9,7 @@ extern void ppc_printk_progress(char *s,
extern unsigned int rtas_data;
extern unsigned long long memory_limit;
+extern bool init_mem_is_free;
extern unsigned long klimit;
extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask);
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -28,6 +28,12 @@ static int __patch_instruction(unsigned
{
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;
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -63,6 +63,7 @@
#endif
unsigned long long memory_limit;
+bool init_mem_is_free;
#ifdef CONFIG_HIGHMEM
pte_t *kmap_pte;
@@ -396,6 +397,7 @@ void free_initmem(void)
{
ppc_md.progress = ppc_printk_progress;
mark_initmem_nx();
+ init_mem_is_free = true;
free_initmem_default(POISON_FREE_INITMEM);
}
