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Subject[tip:x86/timers] x86/alternatives, jumplabel: Use text_poke_early() before mm_init()
Commit-ID:  6fffacb30349e0903602d664f7ab6fc87e85162e
Gitweb: https://git.kernel.org/tip/6fffacb30349e0903602d664f7ab6fc87e85162e
Author: Pavel Tatashin <pasha.tatashin@oracle.com>
AuthorDate: Thu, 19 Jul 2018 16:55:27 -0400
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 20 Jul 2018 00:02:38 +0200

x86/alternatives, jumplabel: Use text_poke_early() before mm_init()

It supposed to be safe to modify static branches after jump_label_init().
But, because static key modifying code eventually calls text_poke() it can
end up accessing a struct page which has not been initialized yet.

Here is how to quickly reproduce the problem. Insert code like this
into init/main.c:

| +static DEFINE_STATIC_KEY_FALSE(__test);
| asmlinkage __visible void __init start_kernel(void)
| {
| char *command_line;
|@@ -587,6 +609,10 @@ asmlinkage __visible void __init start_kernel(void)
| vfs_caches_init_early();
| sort_main_extable();
| trap_init();
|+ {
|+ static_branch_enable(&__test);
|+ WARN_ON(!static_branch_likely(&__test));
|+ }
| mm_init();

The following warnings show-up:
WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:701 text_poke+0x20d/0x230
RIP: 0010:text_poke+0x20d/0x230
Call Trace:
? text_poke_bp+0x50/0xda
? arch_jump_label_transform+0x89/0xe0
? __jump_label_update+0x78/0xb0
? static_key_enable_cpuslocked+0x4d/0x80
? static_key_enable+0x11/0x20
? start_kernel+0x23e/0x4c8
? secondary_startup_64+0xa5/0xb0

---[ end trace abdc99c031b8a90a ]---

If the code above is moved after mm_init(), no warning is shown, as struct
pages are initialized during handover from memblock.

Use text_poke_early() in static branching until early boot IRQs are enabled
and from there switch to text_poke. Also, ensure text_poke() is never
invoked when unitialized memory access may happen by using adding a
!after_bootmem assertion.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: peterz@infradead.org
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-9-pasha.tatashin@oracle.com
---
arch/x86/include/asm/text-patching.h | 1 +
arch/x86/kernel/alternative.c | 7 +++++++
arch/x86/kernel/jump_label.c | 11 +++++++----
3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 2ecd34e2d46c..e85ff65c43c3 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -37,5 +37,6 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
extern void *text_poke(void *addr, const void *opcode, size_t len);
extern int poke_int3_handler(struct pt_regs *regs);
extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
+extern int after_bootmem;

#endif /* _ASM_X86_TEXT_PATCHING_H */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a481763a3776..014f214da581 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -668,6 +668,7 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
local_irq_save(flags);
memcpy(addr, opcode, len);
local_irq_restore(flags);
+ sync_core();
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
return addr;
@@ -693,6 +694,12 @@ void *text_poke(void *addr, const void *opcode, size_t len)
struct page *pages[2];
int i;

+ /*
+ * While boot memory allocator is runnig we cannot use struct
+ * pages as they are not yet initialized.
+ */
+ BUG_ON(!after_bootmem);
+
if (!core_kernel_text((unsigned long)addr)) {
pages[0] = vmalloc_to_page(addr);
pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index e56c95be2808..eeea935e9bb5 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -37,15 +37,18 @@ static void bug_at(unsigned char *ip, int line)
BUG();
}

-static void __jump_label_transform(struct jump_entry *entry,
- enum jump_label_type type,
- void *(*poker)(void *, const void *, size_t),
- int init)
+static void __ref __jump_label_transform(struct jump_entry *entry,
+ enum jump_label_type type,
+ void *(*poker)(void *, const void *, size_t),
+ int init)
{
union jump_code_union code;
const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];

+ if (early_boot_irqs_disabled)
+ poker = text_poke_early;
+
if (type == JUMP_LABEL_JMP) {
if (init) {
/*
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