(2013/07/22 20:14), Jiri Kosina wrote:
> In fd4363fff3d96 ("x86: Introduce int3 (breakpoint)-based instruction
> patching"), the mechanism that was introduced for notifying alternatives
> code from int3 exception handler that and exception occured was
> die_notifier.
>
> This is however problematic, as early code might be using jump labels even
> before the notifier registration has been performed, which will then lead
> to an oops due to unhandled exception. One of such occurences has been
> encountered by Fengguang:
Ah, right!
>
> int3: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> Modules linked in:
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.11.0-rc1-01429-g04bf576 #8
> task: ffff88000da1b040 ti: ffff88000da1c000 task.ti: ffff88000da1c000
> RIP: 0010:[<ffffffff811098cc>] [<ffffffff811098cc>]
> ttwu_do_wakeup+0x28/0x225
> RSP: 0000:ffff88000dd03f10 EFLAGS: 00000006
> RAX: 0000000000000000 RBX: ffff88000dd12940 RCX: ffffffff81769c40
> RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: ffff88000dd03f28 R08: ffffffff8176a8c0 R09: 0000000000000002
> R10: ffffffff810ff484 R11: ffff88000dd129e8 R12: ffff88000dbc90c0
> R13: ffff88000dbc90c0 R14: ffff88000da1dfd8 R15: ffff88000da1dfd8
> FS: 0000000000000000(0000) GS:ffff88000dd00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00000000ffffffff CR3: 0000000001c88000 CR4: 00000000000006e0
> Stack:
> ffff88000dd12940 ffff88000dbc90c0 ffff88000da1dfd8 ffff88000dd03f48
> ffffffff81109e2b ffff88000dd12940 0000000000000000 ffff88000dd03f68
> ffffffff81109e9e 0000000000000000 0000000000012940 ffff88000dd03f98
> Call Trace:
> <IRQ>
> [<ffffffff81109e2b>] ttwu_do_activate.constprop.56+0x6d/0x79
> [<ffffffff81109e9e>] sched_ttwu_pending+0x67/0x84
> [<ffffffff8110c845>] scheduler_ipi+0x15a/0x2b0
> [<ffffffff8104dfb4>] smp_reschedule_interrupt+0x38/0x41
> [<ffffffff8173bf5d>] reschedule_interrupt+0x6d/0x80
> <EOI>
> [<ffffffff810ff484>] ? __atomic_notifier_call_chain+0x5/0xc1
> [<ffffffff8105cc30>] ? native_safe_halt+0xd/0x16
> [<ffffffff81015f10>] default_idle+0x147/0x282
> [<ffffffff81017026>] arch_cpu_idle+0x3d/0x5d
> [<ffffffff81127d6a>] cpu_idle_loop+0x46d/0x5db
> [<ffffffff81127f5c>] cpu_startup_entry+0x84/0x84
> [<ffffffff8104f4f8>] start_secondary+0x3c8/0x3d5
> Code: 5c 5d c3 e8 d7 0f 63 00 55 48 ff 05 1f 5d 1e 01 48 89 e5 41 55 49 89
> f5 41 54 53 48 89 fb e8 8d fe ff ff 48
> 01 cc <1f> 44 00 00 31 c0 eb 0c 48 ff 05 05 5d 1e 01 b8 01 00 00 00 48
> RIP [<ffffffff811098cc>] ttwu_do_wakeup+0x28/0x225
> RSP <ffff88000dd03f10>
> ---[ end trace 0d3288a047152a17 ]---
>
> Fix this by directly calling poke_int3_handler() from the int3 exception
> handler (analogically to what ftrace has been doing already), instead of
> relying on notifier, registration of which might not have yet been
> finalized by the time of the first trap.
This seems OK for me.
Reviewed-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
Thanks!
>
> Reported-and-tested-by: Fengguang Wu <fengguang...@intel.com>
> Signed-off-by: Jiri Kosina <jkos...@suse.cz>
> ---
> arch/x86/include/asm/alternative.h | 2 ++
> arch/x86/kernel/alternative.c | 31 ++++++++-----------------------
> arch/x86/kernel/traps.c | 4 ++++
> kernel/kprobes.c | 2 +-
> 4 files changed, 15 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/include/asm/alternative.h
> b/arch/x86/include/asm/alternative.h
> index 3abf8dd..4df44c2 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -5,6 +5,7 @@
> #include <linux/stddef.h>
> #include <linux/stringify.h>
> #include <asm/asm.h>
> +#include <asm/ptrace.h>
>
> /*
> * Alternative inline assembly for SMP.
> @@ -232,6 +233,7 @@ struct text_poke_param {
> size_t len;
> };
>
> +extern int poke_int3_handler(struct pt_regs *regs);
> extern void *text_poke(void *addr, const void *opcode, size_t len);
> extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void
> *handler);
> extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 0ab4936..7f6351f 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -605,26 +605,24 @@ static void do_sync_core(void *info)
> static bool bp_patching_in_progress;
> static void *bp_int3_handler, *bp_int3_addr;
>
> -static int int3_notify(struct notifier_block *self, unsigned long val, void
> *data)
> +int poke_int3_handler(struct pt_regs *regs)
> {
> - struct die_args *args = data;
> -
> /* bp_patching_in_progress */
> smp_rmb();
>
> if (likely(!bp_patching_in_progress))
> - return NOTIFY_DONE;
> + return 0;
>
> - /* we are not interested in non-int3 faults and ring > 0 faults */
> - if (val != DIE_INT3 || !args->regs || user_mode_vm(args->regs)
> - || args->regs->ip != (unsigned long)bp_int3_addr)
> - return NOTIFY_DONE;
> + if (user_mode_vm(regs) || regs->ip != (unsigned long)bp_int3_addr)
> + return 0;
>
> /* set up the specified breakpoint handler */
> - args->regs->ip = (unsigned long) bp_int3_handler;
> + regs->ip = (unsigned long) bp_int3_handler;
> +
> + return 1;
>
> - return NOTIFY_STOP;
> }
> +
> /**
> * text_poke_bp() -- update instructions on live kernel on SMP
> * @addr: address to patch
> @@ -689,19 +687,6 @@ void *text_poke_bp(void *addr, const void *opcode,
> size_t len, void *handler)
> return addr;
> }
>
> -/* this one needs to run before anything else handles it as a
> - * regular exception */
> -static struct notifier_block int3_nb = {
> - .priority = 0x7fffffff,
> - .notifier_call = int3_notify
> -};
> -
> -static int __init int3_init(void)
> -{
> - return register_die_notifier(&int3_nb);
> -}
> -
> -arch_initcall(int3_init);
> /*
> * Cross-modifying kernel text with stop_machine().
> * This code originally comes from immediate value.
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 772e2a8..2694486 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -58,6 +58,7 @@
> #include <asm/mce.h>
> #include <asm/fixmap.h>
> #include <asm/mach_traps.h>
> +#include <asm/alternative.h>
>
> #ifdef CONFIG_X86_64
> #include <asm/x86_init.h>
> @@ -324,6 +325,9 @@ dotraplinkage void __kprobes notrace do_int3(struct
> pt_regs *regs, long error_co
> ftrace_int3_handler(regs))
> return;
> #endif
> + if (poke_int3_handler(regs))
> + return;
> +
> prev_state = exception_enter();
> #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
> if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d6db7bd..bddf3b2 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1709,7 +1709,7 @@ EXPORT_SYMBOL_GPL(unregister_kprobes);
>
> static struct notifier_block kprobe_exceptions_nb = {
> .notifier_call = kprobe_exceptions_notify,
> - .priority = 0x7ffffff0 /* High priority, but not first. */
> + .priority = 0x7fffffff /* we need to be notified first */
> };
>
> unsigned long __weak arch_deref_entry_point(void *entry)
>
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
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