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

[Michael Ellerman]

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>
---
 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