> It's my understanding that the two pieces of work required to enable live > patching on arm are in flight upstream; > - Reliable stack traces as implemented by Madhavan T. Venkataraman [1] > - Objtool as implemented by Julien Thierry [2] > > This is the remaining part required to enable live patching on arm. > Based on work by Torsten Duwe [3] > > Allocate a task flag used to represent the patch pending state for the > task. Also implement generic functions klp_arch_set_pc() & > klp_get_ftrace_location(). > > In klp_arch_set_pc() it is sufficient to set regs->pc as in > ftrace_common_return() the return address is loaded from the stack. > > ldr x9, [sp, #S_PC] > <snip> > ret x9 > > In klp_get_ftrace_location() it is necessary to advance the address by > AARCH64_INSN_SIZE (4) to point to the BL in the callsite as 2 nops were > placed at the start of the function, one to be patched to save the LR and > another to be patched to branch to the ftrace call, and > klp_get_ftrace_location() is expected to return the address of the BL. It > may also be necessary to advance the address by another AARCH64_INSN_SIZE > if CONFIG_ARM64_BTI_KERNEL is enabled due to the instruction placed at the > branch target to satisfy BTI, > > Signed-off-by: Suraj Jitindar Singh <surajjs@xxxxxxxxxx> > > [1] https://lkml.org/lkml/2021/5/26/1212 > [2] https://lkml.org/lkml/2021/3/3/1135 > [3] https://lkml.org/lkml/2018/10/26/536 > --- AFAIU Madhavan's patch series linked in the above [1] is currently awaiting review by Mark Rutland. It seems that not only this patch series but also the implementation of arch_stack_walk_reliable() at the below link is required to enable livepatch. https://lore.kernel.org/linux-arm-kernel/bf3a5289-8199-b665-0327-ed8240dd7827@xxxxxxxxxxxxxxxxxxx/ > arch/arm64/Kconfig | 3 ++ > arch/arm64/include/asm/livepatch.h | 42 ++++++++++++++++++++++++++++ > arch/arm64/include/asm/thread_info.h | 4 ++- > arch/arm64/kernel/signal.c | 4 +++ > 4 files changed, 52 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/include/asm/livepatch.h > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index b098dabed8c2..c4636990c01d 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -187,6 +187,7 @@ config ARM64 > select HAVE_GCC_PLUGINS > select HAVE_HW_BREAKPOINT if PERF_EVENTS > select HAVE_IRQ_TIME_ACCOUNTING > + select HAVE_LIVEPATCH > select HAVE_NMI > select HAVE_PATA_PLATFORM > select HAVE_PERF_EVENTS > @@ -1946,3 +1947,5 @@ source "arch/arm64/kvm/Kconfig" > if CRYPTO > source "arch/arm64/crypto/Kconfig" > endif > + > +source "kernel/livepatch/Kconfig" I think ` source "kernel/livepatch/Kconfig"` should be placed between `menu "Kernel Features"` and `endmenu`. Thanks Keiya > diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h > new file mode 100644 > index 000000000000..72d7cd86f158 > --- /dev/null > +++ b/arch/arm64/include/asm/livepatch.h > @@ -0,0 +1,42 @@ > +/* SPDX-License-Identifier: GPL-2.0 > + * > + * livepatch.h - arm64-specific Kernel Live Patching Core > + */ > +#ifndef _ASM_ARM64_LIVEPATCH_H > +#define _ASM_ARM64_LIVEPATCH_H > + > +#include <linux/ftrace.h> > + > +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip) > +{ > + struct pt_regs *regs = ftrace_get_regs(fregs); > + > + regs->pc = ip; > +} > + > +/* > + * klp_get_ftrace_location is expected to return the address of the BL to the > + * relevant ftrace handler in the callsite. The location of this can vary based > + * on several compilation options. > + * CONFIG_DYNAMIC_FTRACE_WITH_REGS > + * - Inserts 2 nops on function entry the second of which is the BL > + * referenced above. (See ftrace_init_nop() for the callsite sequence) > + * (this is required by livepatch and must be selected) > + * CONFIG_ARM64_BTI_KERNEL: > + * - Inserts a hint #0x22 on function entry if the function is called > + * indirectly (to satisfy BTI requirements), which is inserted before > + * the two nops from above. > + */ > +#define klp_get_ftrace_location klp_get_ftrace_location > +static inline unsigned long klp_get_ftrace_location(unsigned long faddr) > +{ > + unsigned long addr = faddr + AARCH64_INSN_SIZE; > + > +#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) > + addr = ftrace_location_range(addr, addr + AARCH64_INSN_SIZE); > +#endif > + > + return addr; > +} > + > +#endif /* _ASM_ARM64_LIVEPATCH_H */ > diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h > index 6623c99f0984..cca936d53a40 100644 > --- a/arch/arm64/include/asm/thread_info.h > +++ b/arch/arm64/include/asm/thread_info.h > @@ -67,6 +67,7 @@ int arch_dup_task_struct(struct task_struct *dst, > #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */ > #define TIF_MTE_ASYNC_FAULT 5 /* MTE Asynchronous Tag Check Fault */ > #define TIF_NOTIFY_SIGNAL 6 /* signal notifications exist */ > +#define TIF_PATCH_PENDING 7 /* pending live patching update */ > #define TIF_SYSCALL_TRACE 8 /* syscall trace active */ > #define TIF_SYSCALL_AUDIT 9 /* syscall auditing */ > #define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */ > @@ -97,11 +98,12 @@ int arch_dup_task_struct(struct task_struct *dst, > #define _TIF_SVE (1 << TIF_SVE) > #define _TIF_MTE_ASYNC_FAULT (1 << TIF_MTE_ASYNC_FAULT) > #define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL) > +#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING) > > #define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ > _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \ > _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \ > - _TIF_NOTIFY_SIGNAL) > + _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING) > > #define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ > _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \ > diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c > index 6237486ff6bb..d1eedb0589a7 100644 > --- a/arch/arm64/kernel/signal.c > +++ b/arch/arm64/kernel/signal.c > @@ -18,6 +18,7 @@ > #include <linux/sizes.h> > #include <linux/string.h> > #include <linux/tracehook.h> > +#include <linux/livepatch.h> > #include <linux/ratelimit.h> > #include <linux/syscalls.h> > > @@ -932,6 +933,9 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, > (void __user *)NULL, current); > } > > + if (thread_flags & _TIF_PATCH_PENDING) > + klp_update_patch_state(current); > + > if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) > do_signal(regs); > > -- > 2.17.1
