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3b23e4991f
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
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| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
109 lines
2.9 KiB
C
109 lines
2.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* arch/arm64/include/asm/ftrace.h
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*
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* Copyright (C) 2013 Linaro Limited
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* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
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*/
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#ifndef __ASM_FTRACE_H
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#define __ASM_FTRACE_H
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#include <asm/insn.h>
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#define HAVE_FUNCTION_GRAPH_FP_TEST
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#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
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#define ARCH_SUPPORTS_FTRACE_OPS 1
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#else
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#define MCOUNT_ADDR ((unsigned long)_mcount)
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#endif
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/* The BL at the callsite's adjusted rec->ip */
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#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
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#define FTRACE_PLT_IDX 0
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#define FTRACE_REGS_PLT_IDX 1
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#define NR_FTRACE_PLTS 2
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/*
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* Currently, gcc tends to save the link register after the local variables
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* on the stack. This causes the max stack tracer to report the function
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* frame sizes for the wrong functions. By defining
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* ARCH_FTRACE_SHIFT_STACK_TRACER, it will tell the stack tracer to expect
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* to find the return address on the stack after the local variables have
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* been set up.
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*
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* Note, this may change in the future, and we will need to deal with that
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* if it were to happen.
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*/
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#define ARCH_FTRACE_SHIFT_STACK_TRACER 1
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#ifndef __ASSEMBLY__
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#include <linux/compat.h>
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extern void _mcount(unsigned long);
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extern void *return_address(unsigned int);
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struct dyn_arch_ftrace {
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/* No extra data needed for arm64 */
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};
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extern unsigned long ftrace_graph_call;
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extern void return_to_handler(void);
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static inline unsigned long ftrace_call_adjust(unsigned long addr)
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{
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/*
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* Adjust addr to point at the BL in the callsite.
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* See ftrace_init_nop() for the callsite sequence.
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*/
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if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
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return addr + AARCH64_INSN_SIZE;
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/*
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* addr is the address of the mcount call instruction.
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* recordmcount does the necessary offset calculation.
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*/
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return addr;
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}
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#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
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struct dyn_ftrace;
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int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
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#define ftrace_init_nop ftrace_init_nop
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#endif
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#define ftrace_return_address(n) return_address(n)
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/*
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* Because AArch32 mode does not share the same syscall table with AArch64,
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* tracing compat syscalls may result in reporting bogus syscalls or even
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* hang-up, so just do not trace them.
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* See kernel/trace/trace_syscalls.c
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*
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* x86 code says:
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* If the user really wants these, then they should use the
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* raw syscall tracepoints with filtering.
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*/
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#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
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static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs)
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{
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return is_compat_task();
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}
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#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
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static inline bool arch_syscall_match_sym_name(const char *sym,
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const char *name)
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{
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/*
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* Since all syscall functions have __arm64_ prefix, we must skip it.
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* However, as we described above, we decided to ignore compat
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* syscalls, so we don't care about __arm64_compat_ prefix here.
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*/
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return !strcmp(sym + 8, name);
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}
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#endif /* ifndef __ASSEMBLY__ */
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#endif /* __ASM_FTRACE_H */
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