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![Nathan Chancellor](/assets/img/avatar_default.png)
Clang warns: ../kernel/extable.c:37:52: warning: array comparison always evaluates to a constant [-Wtautological-compare] if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) { ^ 1 warning generated. These are not true arrays, they are linker defined symbols, which are just addresses. Using the address of operator silences the warning and does not change the resulting assembly with either clang/ld.lld or gcc/ld (tested with diff + objdump -Dr). Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Link: https://github.com/ClangBuiltLinux/linux/issues/892 Link: http://lkml.kernel.org/r/20200219202036.45702-1-natechancellor@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
175 lines
4.4 KiB
C
175 lines
4.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Rewritten by Rusty Russell, on the backs of many others...
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Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.
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*/
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#include <linux/ftrace.h>
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#include <linux/memory.h>
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#include <linux/extable.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/init.h>
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#include <linux/kprobes.h>
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#include <linux/filter.h>
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#include <asm/sections.h>
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#include <linux/uaccess.h>
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/*
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* mutex protecting text section modification (dynamic code patching).
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* some users need to sleep (allocating memory...) while they hold this lock.
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*
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* Note: Also protects SMP-alternatives modification on x86.
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*
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* NOT exported to modules - patching kernel text is a really delicate matter.
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*/
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DEFINE_MUTEX(text_mutex);
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extern struct exception_table_entry __start___ex_table[];
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extern struct exception_table_entry __stop___ex_table[];
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/* Cleared by build time tools if the table is already sorted. */
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u32 __initdata __visible main_extable_sort_needed = 1;
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/* Sort the kernel's built-in exception table */
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void __init sort_main_extable(void)
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{
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if (main_extable_sort_needed &&
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&__stop___ex_table > &__start___ex_table) {
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pr_notice("Sorting __ex_table...\n");
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sort_extable(__start___ex_table, __stop___ex_table);
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}
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}
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/* Given an address, look for it in the kernel exception table */
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const
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struct exception_table_entry *search_kernel_exception_table(unsigned long addr)
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{
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return search_extable(__start___ex_table,
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__stop___ex_table - __start___ex_table, addr);
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}
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/* Given an address, look for it in the exception tables. */
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const struct exception_table_entry *search_exception_tables(unsigned long addr)
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{
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const struct exception_table_entry *e;
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e = search_kernel_exception_table(addr);
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if (!e)
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e = search_module_extables(addr);
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if (!e)
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e = search_bpf_extables(addr);
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return e;
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}
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int init_kernel_text(unsigned long addr)
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{
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if (addr >= (unsigned long)_sinittext &&
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addr < (unsigned long)_einittext)
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return 1;
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return 0;
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}
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int notrace core_kernel_text(unsigned long addr)
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{
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if (addr >= (unsigned long)_stext &&
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addr < (unsigned long)_etext)
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return 1;
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if (system_state < SYSTEM_RUNNING &&
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init_kernel_text(addr))
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return 1;
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return 0;
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}
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/**
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* core_kernel_data - tell if addr points to kernel data
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* @addr: address to test
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*
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* Returns true if @addr passed in is from the core kernel data
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* section.
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*
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* Note: On some archs it may return true for core RODATA, and false
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* for others. But will always be true for core RW data.
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*/
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int core_kernel_data(unsigned long addr)
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{
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if (addr >= (unsigned long)_sdata &&
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addr < (unsigned long)_edata)
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return 1;
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return 0;
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}
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int __kernel_text_address(unsigned long addr)
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{
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if (kernel_text_address(addr))
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return 1;
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/*
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* There might be init symbols in saved stacktraces.
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* Give those symbols a chance to be printed in
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* backtraces (such as lockdep traces).
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*
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* Since we are after the module-symbols check, there's
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* no danger of address overlap:
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*/
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if (init_kernel_text(addr))
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return 1;
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return 0;
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}
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int kernel_text_address(unsigned long addr)
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{
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bool no_rcu;
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int ret = 1;
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if (core_kernel_text(addr))
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return 1;
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/*
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* If a stack dump happens while RCU is not watching, then
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* RCU needs to be notified that it requires to start
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* watching again. This can happen either by tracing that
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* triggers a stack trace, or a WARN() that happens during
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* coming back from idle, or cpu on or offlining.
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*
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* is_module_text_address() as well as the kprobe slots,
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* is_bpf_text_address() and is_bpf_image_address require
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* RCU to be watching.
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*/
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no_rcu = !rcu_is_watching();
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/* Treat this like an NMI as it can happen anywhere */
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if (no_rcu)
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rcu_nmi_enter();
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if (is_module_text_address(addr))
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goto out;
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if (is_ftrace_trampoline(addr))
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goto out;
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if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
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goto out;
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if (is_bpf_text_address(addr))
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goto out;
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ret = 0;
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out:
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if (no_rcu)
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rcu_nmi_exit();
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return ret;
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}
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/*
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* On some architectures (PPC64, IA64) function pointers
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* are actually only tokens to some data that then holds the
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* real function address. As a result, to find if a function
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* pointer is part of the kernel text, we need to do some
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* special dereferencing first.
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*/
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int func_ptr_is_kernel_text(void *ptr)
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{
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unsigned long addr;
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addr = (unsigned long) dereference_function_descriptor(ptr);
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if (core_kernel_text(addr))
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return 1;
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return is_module_text_address(addr);
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}
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