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b64913394f
WRITE_KERN is supposed to overwrite some kernel text, namely do_overwritten() function. But at the time being it overwrites do_overwritten() function descriptor, not function text. Fix it by dereferencing the function descriptor to obtain function text pointer. Export dereference_function_descriptor() for when LKDTM is built as a module. And make do_overwritten() noinline so that it is really do_overwritten() which is called by lkdtm_WRITE_KERN(). Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/31e58eaffb5bc51c07d8d4891d1982100ade8cfc.1644928018.git.christophe.leroy@csgroup.eu
171 lines
4.3 KiB
C
171 lines
4.3 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/elf.h>
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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 notrace core_kernel_text(unsigned long addr)
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{
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if (is_kernel_text(addr))
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return 1;
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if (system_state < SYSTEM_FREEING_INITMEM &&
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is_kernel_inittext(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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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 (is_kernel_inittext(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, PARISC) 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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#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
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void *dereference_function_descriptor(void *ptr)
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{
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func_desc_t *desc = ptr;
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void *p;
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if (!get_kernel_nofault(p, (void *)&desc->addr))
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ptr = p;
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return ptr;
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}
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EXPORT_SYMBOL_GPL(dereference_function_descriptor);
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void *dereference_kernel_function_descriptor(void *ptr)
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{
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if (ptr < (void *)__start_opd || ptr >= (void *)__end_opd)
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return ptr;
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return dereference_function_descriptor(ptr);
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}
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#endif
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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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