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SubjectRe: [PATCH v4 2/3] arm64: implement live patching
On 26 October 2018 at 16:21, Torsten Duwe <duwe@lst.de> wrote:
> Based on ftrace with regs, do the usual thing.
> (see Documentation/livepatch/livepatch.txt)
>
> Use task flag bit 6 to track patch transisiton state for the consistency
> model. Add it to the work mask so it gets cleared on all kernel exits to
> userland.
>
> Tell livepatch regs->pc is the place to change the return address.
> Make sure the graph tracer call hook is only called on the final function
> entry in case regs->pc gets modified after an interception.
>
> Signed-off-by: Torsten Duwe <duwe@suse.de>
>
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -120,6 +120,7 @@ config ARM64
> select HAVE_GENERIC_DMA_COHERENT
> select HAVE_HW_BREAKPOINT if PERF_EVENTS
> select HAVE_IRQ_TIME_ACCOUNTING
> + select HAVE_LIVEPATCH
> select HAVE_MEMBLOCK
> select HAVE_MEMBLOCK_NODE_MAP if NUMA
> select HAVE_NMI
> @@ -1350,4 +1351,6 @@ if CRYPTO
> source "arch/arm64/crypto/Kconfig"
> endif
>
> +source "kernel/livepatch/Kconfig"
> +
> source "lib/Kconfig"
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -76,6 +76,7 @@ void arch_release_task_struct(struct tas
> #define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
> #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
> #define TIF_FSCHECK 5 /* Check FS is USER_DS on return */
> +#define TIF_PATCH_PENDING 6
> #define TIF_NOHZ 7
> #define TIF_SYSCALL_TRACE 8
> #define TIF_SYSCALL_AUDIT 9
> @@ -94,6 +95,7 @@ void arch_release_task_struct(struct tas
> #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
> #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
> #define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
> +#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
> #define _TIF_NOHZ (1 << TIF_NOHZ)
> #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
> #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
> @@ -106,7 +108,8 @@ void arch_release_task_struct(struct tas
>
> #define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
> _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
> - _TIF_UPROBE | _TIF_FSCHECK)
> + _TIF_UPROBE | _TIF_FSCHECK | \
> + _TIF_PATCH_PENDING)
>
> #define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
> _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
> --- /dev/null
> +++ b/arch/arm64/include/asm/livepatch.h
> @@ -0,0 +1,35 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * livepatch.h - arm64-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2016,2018 SUSE
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef _ASM_ARM64_LIVEPATCH_H
> +#define _ASM_ARM64_LIVEPATCH_H
> +
> +#include <asm/ptrace.h>
> +
> +static inline int klp_check_compiler_support(void)
> +{
> + return 0;
> +}
> +
> +static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +{
> + regs->pc = ip;
> +}
> +
> +#endif /* _ASM_ARM64_LIVEPATCH_H */
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -226,6 +226,7 @@ ftrace_common:
>
> /* The program counter just after the ftrace call site */
> str lr, [x9, #S_PC]
> +
> /* The stack pointer as it was on ftrace_caller entry... */
> add x28, fp, #16
> str x28, [x9, #S_SP]

Please drop this hunk

> @@ -233,6 +234,10 @@ ftrace_common:
> ldr x28, [fp, 8]
> str x28, [x9, #S_LR] /* to pt_regs.r[30] */
>
> +#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_FUNCTION_GRAPH_TRACER)
> + mov x28, lr /* remember old return address */
> +#endif
> +
> ldr_l x2, function_trace_op, x0
> ldr x1, [fp, #8]
> sub x0, lr, #8 /* function entry == IP */
> @@ -245,6 +250,17 @@ ftrace_call:
>
> bl ftrace_stub
>
> +#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_FUNCTION_GRAPH_TRACER)
> + /* Is the trace function a live patcher an has messed with
> + * the return address?
> + */
> + add x9, sp, #16 /* advance to pt_regs for restore */
> + ldr x0, [x9, #S_PC]
> + cmp x0, x28 /* compare with the value we remembered */
> + /* to not call graph tracer's "call" mechanism twice! */
> + b.ne ftrace_common_return

Is ftrace_common_return guaranteed to be in range? Conditional
branches have only -/+ 1 MB range IIRC.

Better to do

b.eq ftrace_graph_call
b ftrace_common_return

to be sure

> +#endif
> +
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER

Can we fold these #ifdef blocks together (i.e, incorporate the
conditional livepatch sequence here)

> .global ftrace_graph_call
> ftrace_graph_call: // ftrace_graph_caller();
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -29,6 +29,7 @@
> #include <linux/sizes.h>
> #include <linux/string.h>
> #include <linux/tracehook.h>
> +#include <linux/livepatch.h>
> #include <linux/ratelimit.h>
> #include <linux/syscalls.h>
>
> @@ -934,6 +935,9 @@ asmlinkage void do_notify_resume(struct
> if (thread_flags & _TIF_UPROBE)
> uprobe_notify_resume(regs);
>
> + if (thread_flags & _TIF_PATCH_PENDING)
> + klp_update_patch_state(current);
> +
> if (thread_flags & _TIF_SIGPENDING)
> do_signal(regs);
>

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