Messages in this thread Patch in this message | | | From | Josh Poimboeuf <> | Subject | [PATCH 11/19] x86/dumptrace: add new unwind interface and implementations | Date | Thu, 21 Jul 2016 16:21:48 -0500 |
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The x86 stack dump code is a bit of a mess. dump_trace() uses callbacks, and each user of it seems to have slightly different requirements, so there are several slightly different callbacks floating around.
Also there are some upcoming features which will require more changes to the stack dump code: reliable stack detection for live patching, hardened user copy, and the DWARF unwinder. Each of those features would at least need more callbacks and/or callback interfaces, resulting in a much bigger mess than what we have today.
Before doing all that, we should try to clean things up and replace dump_trace() with something cleaner and more flexible.
The new unwinder is a simple state machine which was heavily inspired by a suggestion from Andy Lutomirski:
https://lkml.kernel.org/r/CALCETrUbNTqaM2LRyXGRx=kVLRPeY5A3Pc6k4TtQxF320rUT=w@mail.gmail.com
It's also very similar to the libunwind API:
http://www.nongnu.org/libunwind/man/libunwind(3).html
Some if its advantages:
- Simplicity: no more callback sprawl and less code duplication.
- Flexibility: it allows the caller to stop and inspect the stack state at each step in the unwinding process.
- Modularity: the unwinder code, console stack dump code, and stack metadata analysis code are all better separated so that changing one of them shouldn't have much of an impact on any of the others.
Two implementations are added which conform to the new unwind interface:
- The frame pointer unwinder which is used for CONFIG_FRAME_POINTER=y.
- The "guess" unwinder which is used for CONFIG_FRAME_POINTER=n. This isn't an "unwinder" per se. All it does is scan the stack for kernel text addresses. But with no frame pointers, guesses are better than nothing in most cases.
Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> --- arch/x86/include/asm/unwind.h | 80 +++++++++++++++++++++++++++++++++++++ arch/x86/kernel/Makefile | 6 +++ arch/x86/kernel/unwind_frame.c | 89 ++++++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/unwind_guess.c | 40 +++++++++++++++++++ 4 files changed, 215 insertions(+) create mode 100644 arch/x86/include/asm/unwind.h create mode 100644 arch/x86/kernel/unwind_frame.c create mode 100644 arch/x86/kernel/unwind_guess.c
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h new file mode 100644 index 0000000..61c6e95 --- /dev/null +++ b/arch/x86/include/asm/unwind.h @@ -0,0 +1,80 @@ +#ifndef _ASM_X86_UNWIND_H +#define _ASM_X86_UNWIND_H + +#include <linux/sched.h> +#include <linux/ftrace.h> +#include <asm/ptrace.h> +#include <asm/stacktrace.h> + +struct unwind_state { + struct stack_info stack_info; + unsigned long stack_mask; + struct task_struct *task; + unsigned long *sp; + int graph_idx; +#ifdef CONFIG_FRAME_POINTER + unsigned long *bp; +#endif +}; + +void __unwind_start(struct unwind_state *state, struct task_struct *task, + struct pt_regs *regs, unsigned long *sp); + +bool unwind_next_frame(struct unwind_state *state); + + +#ifdef CONFIG_FRAME_POINTER + +static inline unsigned long *unwind_get_return_address_ptr(struct unwind_state *state) +{ + if (state->stack_info.type == STACK_TYPE_UNKNOWN) + return NULL; + + return state->bp + 1; +} + +unsigned long unwind_get_return_address(struct unwind_state *state); + +#else /* !CONFIG_FRAME_POINTER */ + +static inline unsigned long *unwind_get_return_address_ptr(struct unwind_state *state) +{ + return NULL; +} + +static inline unsigned long unwind_get_return_address(struct unwind_state *state) +{ + if (state->stack_info.type == STACK_TYPE_UNKNOWN) + return 0; + + return *state->sp; +} + +#endif /* CONFIG_FRAME_POINTER */ + +static inline unsigned long *unwind_get_stack_ptr(struct unwind_state *state) +{ + if (state->stack_info.type == STACK_TYPE_UNKNOWN) + return NULL; + + return state->sp; +} + +static inline bool unwind_done(struct unwind_state *state) +{ + return (state->stack_info.type == STACK_TYPE_UNKNOWN); +} + +static inline +void unwind_start(struct unwind_state *state, struct task_struct *task, + struct pt_regs *regs, unsigned long *sp) +{ + if (!task) + task = current; + + sp = sp ? : get_stack_pointer(task, regs); + + __unwind_start(state, task, regs, sp); +} + +#endif /* _ASM_X86_UNWIND_H */ diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 0503f5b..45257cf 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -125,6 +125,12 @@ obj-$(CONFIG_EFI) += sysfb_efi.o obj-$(CONFIG_PERF_EVENTS) += perf_regs.o obj-$(CONFIG_TRACING) += tracepoint.o +ifdef CONFIG_FRAME_POINTER +obj-y += unwind_frame.o +else +obj-y += unwind_guess.o +endif + ### # 64 bit specific files ifeq ($(CONFIG_X86_64),y) diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c new file mode 100644 index 0000000..1234480 --- /dev/null +++ b/arch/x86/kernel/unwind_frame.c @@ -0,0 +1,89 @@ +#include <linux/sched.h> +#include <asm/ptrace.h> +#include <asm/bitops.h> +#include <asm/stacktrace.h> +#include <asm/unwind.h> + +unsigned long unwind_get_return_address(struct unwind_state *state) +{ + unsigned long addr, graph_addr; + + if (state->stack_info.type == STACK_TYPE_UNKNOWN) + return 0; + + addr = *unwind_get_return_address_ptr(state); + graph_addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, + addr); + return graph_addr ? : addr; +} +EXPORT_SYMBOL_GPL(unwind_get_return_address); + +static unsigned long *update_stack_state(struct unwind_state *state, void *addr, + size_t len) +{ + struct stack_info *info = &state->stack_info; + unsigned long *sp; + + if (on_stack(info, addr, len)) + return addr; + + sp = info->next; + if (!sp) + goto unknown; + + if (get_stack_info(sp, state->task, info, &state->stack_mask)) + goto unknown; + + if (!on_stack(info, addr, len)) + goto unknown; + + return sp; + +unknown: + info->type = STACK_TYPE_UNKNOWN; + return NULL; +} + +static bool unwind_next_frame_bp(struct unwind_state *state, unsigned long *bp) +{ + unsigned long *sp; + + sp = update_stack_state(state, bp, sizeof(*bp) * 2); + if (state->stack_info.type == STACK_TYPE_UNKNOWN) + return false; + + state->bp = bp; + state->sp = sp; + + return true; +} + +bool unwind_next_frame(struct unwind_state *state) +{ + unsigned long *bp; + + if (unwind_done(state)) + return false; + + bp = (unsigned long *)*state->bp; + + return unwind_next_frame_bp(state, bp); +} +EXPORT_SYMBOL_GPL(unwind_next_frame); + +void __unwind_start(struct unwind_state *state, struct task_struct *task, + struct pt_regs *regs, unsigned long *sp) +{ + memset(state, 0, sizeof(*state)); + + state->task = task; + state->sp = sp; + state->bp = get_frame_pointer(task, regs); + + get_stack_info(sp, state->task, &state->stack_info, &state->stack_mask); + + /* unwind to the first frame after the user-specified stack pointer */ + while (state->bp < sp && !unwind_done(state)) + unwind_next_frame(state); +} +EXPORT_SYMBOL_GPL(__unwind_start); diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c new file mode 100644 index 0000000..223d020 --- /dev/null +++ b/arch/x86/kernel/unwind_guess.c @@ -0,0 +1,40 @@ +#include <linux/sched.h> +#include <linux/ftrace.h> +#include <asm/ptrace.h> +#include <asm/bitops.h> +#include <asm/stacktrace.h> +#include <asm/unwind.h> + +bool unwind_next_frame(struct unwind_state *state) +{ + struct stack_info *info = &state->stack_info; + + if (info->type == STACK_TYPE_UNKNOWN) + return false; + + do { + for (state->sp++; state->sp < info->end; state->sp++) + if (__kernel_text_address(*state->sp)) + return true; + + state->sp = info->next; + + } while (!get_stack_info(state->sp, state->task, info, + &state->stack_mask)); + + return false; +} + +void __unwind_start(struct unwind_state *state, struct task_struct *task, + struct pt_regs *regs, unsigned long *sp) +{ + memset(state, 0, sizeof(*state)); + + state->task = task; + state->sp = sp; + + get_stack_info(sp, state->task, &state->stack_info, &state->stack_mask); + + if (!__kernel_text_address(*sp)) + unwind_next_frame(state); +} -- 2.7.4
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