Staging
v0.7.0
v0.7.0
https://github.com/torvalds/linux
Tip revision: 6d796c50f84ca79f1722bb131799e5a5710c4700 authored by Linus Torvalds on 29 January 2023, 21:59:43 UTC
Linux 6.2-rc6
Linux 6.2-rc6
Tip revision: 6d796c5
ftrace.c
// SPDX-License-Identifier: GPL-2.0
/*
* Dynamic function tracer architecture backend.
*
* Copyright IBM Corp. 2009,2014
*
* Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
*/
#include <linux/moduleloader.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include <asm/text-patching.h>
#include <asm/cacheflush.h>
#include <asm/ftrace.lds.h>
#include <asm/nospec-branch.h>
#include <asm/set_memory.h>
#include "entry.h"
#include "ftrace.h"
/*
* To generate function prologue either gcc's hotpatch feature (since gcc 4.8)
* or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags
* (since gcc 9 / clang 10) is used.
* In both cases the original and also the disabled function prologue contains
* only a single six byte instruction and looks like this:
* > brcl 0,0 # offset 0
* To enable ftrace the code gets patched like above and afterwards looks
* like this:
* > brasl %r0,ftrace_caller # offset 0
*
* The instruction will be patched by ftrace_make_call / ftrace_make_nop.
* The ftrace function gets called with a non-standard C function call ABI
* where r0 contains the return address. It is also expected that the called
* function only clobbers r0 and r1, but restores r2-r15.
* For module code we can't directly jump to ftrace caller, but need a
* trampoline (ftrace_plt), which clobbers also r1.
*/
void *ftrace_func __read_mostly = ftrace_stub;
struct ftrace_insn {
u16 opc;
s32 disp;
} __packed;
asm(
" .align 16\n"
"ftrace_shared_hotpatch_trampoline_br:\n"
" lmg %r0,%r1,2(%r1)\n"
" br %r1\n"
"ftrace_shared_hotpatch_trampoline_br_end:\n"
);
#ifdef CONFIG_EXPOLINE
asm(
" .align 16\n"
"ftrace_shared_hotpatch_trampoline_exrl:\n"
" lmg %r0,%r1,2(%r1)\n"
" exrl %r0,0f\n"
" j .\n"
"0: br %r1\n"
"ftrace_shared_hotpatch_trampoline_exrl_end:\n"
);
#endif /* CONFIG_EXPOLINE */
#ifdef CONFIG_MODULES
static char *ftrace_plt;
#endif /* CONFIG_MODULES */
static const char *ftrace_shared_hotpatch_trampoline(const char **end)
{
const char *tstart, *tend;
tstart = ftrace_shared_hotpatch_trampoline_br;
tend = ftrace_shared_hotpatch_trampoline_br_end;
#ifdef CONFIG_EXPOLINE
if (!nospec_disable) {
tstart = ftrace_shared_hotpatch_trampoline_exrl;
tend = ftrace_shared_hotpatch_trampoline_exrl_end;
}
#endif /* CONFIG_EXPOLINE */
if (end)
*end = tend;
return tstart;
}
bool ftrace_need_init_nop(void)
{
return true;
}
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
__ftrace_hotpatch_trampolines_start;
static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
static struct ftrace_hotpatch_trampoline *trampoline;
struct ftrace_hotpatch_trampoline **next_trampoline;
struct ftrace_hotpatch_trampoline *trampolines_end;
struct ftrace_hotpatch_trampoline tmp;
struct ftrace_insn *insn;
const char *shared;
s32 disp;
BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
next_trampoline = &next_vmlinux_trampoline;
trampolines_end = __ftrace_hotpatch_trampolines_end;
shared = ftrace_shared_hotpatch_trampoline(NULL);
#ifdef CONFIG_MODULES
if (mod) {
next_trampoline = &mod->arch.next_trampoline;
trampolines_end = mod->arch.trampolines_end;
shared = ftrace_plt;
}
#endif
if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
return -ENOMEM;
trampoline = (*next_trampoline)++;
/* Check for the compiler-generated fentry nop (brcl 0, .). */
if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
return -EINVAL;
/* Generate the trampoline. */
tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
tmp.interceptor = FTRACE_ADDR;
tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
s390_kernel_write(trampoline, &tmp, sizeof(tmp));
/* Generate a jump to the trampoline. */
disp = ((char *)trampoline - (char *)rec->ip) / 2;
insn = (struct ftrace_insn *)rec->ip;
s390_kernel_write(&insn->disp, &disp, sizeof(disp));
return 0;
}
static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
{
struct ftrace_hotpatch_trampoline *trampoline;
struct ftrace_insn insn;
s64 disp;
u16 opc;
if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
return ERR_PTR(-EFAULT);
disp = (s64)insn.disp * 2;
trampoline = (void *)(rec->ip + disp);
if (get_kernel_nofault(opc, &trampoline->brasl_opc))
return ERR_PTR(-EFAULT);
if (opc != 0xc015)
return ERR_PTR(-EINVAL);
return trampoline;
}
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
struct ftrace_hotpatch_trampoline *trampoline;
u64 old;
trampoline = ftrace_get_trampoline(rec);
if (IS_ERR(trampoline))
return PTR_ERR(trampoline);
if (get_kernel_nofault(old, &trampoline->interceptor))
return -EFAULT;
if (old != old_addr)
return -EINVAL;
s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
return 0;
}
static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
{
u16 old;
u8 op;
if (get_kernel_nofault(old, addr))
return -EFAULT;
if (old != expected)
return -EINVAL;
/* set mask field to all ones or zeroes */
op = enable ? 0xf4 : 0x04;
s390_kernel_write((char *)addr + 1, &op, sizeof(op));
return 0;
}
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
/* Expect brcl 0xf,... */
return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
struct ftrace_hotpatch_trampoline *trampoline;
trampoline = ftrace_get_trampoline(rec);
if (IS_ERR(trampoline))
return PTR_ERR(trampoline);
s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
/* Expect brcl 0x0,... */
return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
ftrace_func = func;
return 0;
}
void arch_ftrace_update_code(int command)
{
ftrace_modify_all_code(command);
}
void ftrace_arch_code_modify_post_process(void)
{
/*
* Flush any pre-fetched instructions on all
* CPUs to make the new code visible.
*/
text_poke_sync_lock();
}
#ifdef CONFIG_MODULES
static int __init ftrace_plt_init(void)
{
const char *start, *end;
ftrace_plt = module_alloc(PAGE_SIZE);
if (!ftrace_plt)
panic("cannot allocate ftrace plt\n");
start = ftrace_shared_hotpatch_trampoline(&end);
memcpy(ftrace_plt, start, end - start);
set_memory_ro((unsigned long)ftrace_plt, 1);
return 0;
}
device_initcall(ftrace_plt_init);
#endif /* CONFIG_MODULES */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
* Hook the return address and push it in the stack of return addresses
* in current thread info.
*/
unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
unsigned long ip)
{
if (unlikely(ftrace_graph_is_dead()))
goto out;
if (unlikely(atomic_read(¤t->tracing_graph_pause)))
goto out;
ip -= MCOUNT_INSN_SIZE;
if (!function_graph_enter(ra, ip, 0, (void *) sp))
ra = (unsigned long) return_to_handler;
out:
return ra;
}
NOKPROBE_SYMBOL(prepare_ftrace_return);
/*
* Patch the kernel code at ftrace_graph_caller location. The instruction
* there is branch relative on condition. To enable the ftrace graph code
* block, we simply patch the mask field of the instruction to zero and
* turn the instruction into a nop.
* To disable the ftrace graph code the mask field will be patched to
* all ones, which turns the instruction into an unconditional branch.
*/
int ftrace_enable_ftrace_graph_caller(void)
{
int rc;
/* Expect brc 0xf,... */
rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
if (rc)
return rc;
text_poke_sync_lock();
return 0;
}
int ftrace_disable_ftrace_graph_caller(void)
{
int rc;
/* Expect brc 0x0,... */
rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
if (rc)
return rc;
text_poke_sync_lock();
return 0;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#ifdef CONFIG_KPROBES_ON_FTRACE
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
struct kprobe_ctlblk *kcb;
struct pt_regs *regs;
struct kprobe *p;
int bit;
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
regs = ftrace_get_regs(fregs);
p = get_kprobe((kprobe_opcode_t *)ip);
if (!regs || unlikely(!p) || kprobe_disabled(p))
goto out;
if (kprobe_running()) {
kprobes_inc_nmissed_count(p);
goto out;
}
__this_cpu_write(current_kprobe, p);
kcb = get_kprobe_ctlblk();
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
instruction_pointer_set(regs, ip);
if (!p->pre_handler || !p->pre_handler(p, regs)) {
instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
if (unlikely(p->post_handler)) {
kcb->kprobe_status = KPROBE_HIT_SSDONE;
p->post_handler(p, regs, 0);
}
}
__this_cpu_write(current_kprobe, NULL);
out:
ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
p->ainsn.insn = NULL;
return 0;
}
#endif