[PATCH stable v4.9 04/35] powerpc: Avoid code patching freed init sections

Michael Ellerman
2019-04-11T11:46:41Z

From: Michael Neuling <mikey@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: stable@vger.kernel.org # 4.13+
Signed-off-by: Michael Neuling <mikey@neuling.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/include/asm/setup.h | 1 +
arch/powerpc/lib/code-patching.c | 8 ++++++++
arch/powerpc/mm/mem.c | 2 ++
3 files changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h
index 703ddf752516..709f4e739ae8 100644
--- a/arch/powerpc/include/asm/setup.h
+++ b/arch/powerpc/include/asm/setup.h
@@ -8,6 +8,7 @@ extern void ppc_printk_progress(char *s, unsigned short hex);

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);

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 753d591f1b52..c77c486fbf24 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -14,12 +14,20 @@
#include <asm/page.h>
#include <asm/code-patching.h>
#include <asm/uaccess.h>
+#include <asm/setup.h>
+#include <asm/sections.h>

int patch_instruction(unsigned int *addr, unsigned int instr)
{
int err;

+ /* Make sure we aren't patching a freed init section */
+ if (init_mem_is_free && init_section_contains(addr, 4)) {
+ pr_debug("Skipping init section patching addr: 0x%px\n", addr);
+ return 0;
+ }
+
__put_user_size(instr, addr, 4, err);
if (err)
return err;
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 5f844337de21..1e93dbc88e80 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -62,6 +62,7 @@
#endif

unsigned long long memory_limit;
+bool init_mem_is_free;

#ifdef CONFIG_HIGHMEM
pte_t *kmap_pte;
@@ -396,6 +397,7 @@ void __init mem_init(void)
void free_initmem(void)
{
ppc_md.progress = ppc_printk_progress;
+ init_mem_is_free = true;
free_initmem_default(POISON_FREE_INITMEM);
}

--
2.20.1