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powerpc/ftrace: Simplify ftrace_make_nop()
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Now that we validate the ftrace location during initialization in
ftrace_init_nop(), we can simplify ftrace_make_nop() to patch-in the nop
without worrying about the instructions surrounding the ftrace location.
Note that we continue to ensure that we have a bl to
ftrace_[regs_]caller at the ftrace location before nop-ing it out.

Signed-off-by: Naveen N Rao <naveen@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/e12ccbf28c50c3a07fb614f4d392e55f7098a729.1687166935.git.naveen@kernel.org
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@rnav @mpe
rnav authored and mpe committed Aug 21, 2023
1 parent cc93b92 commit 562bde0
Showing 1 changed file with 32 additions and 188 deletions.
220 changes: 32 additions & 188 deletions arch/powerpc/kernel/trace/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -116,112 +116,6 @@ static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
return ip + (long)offset;
}

#ifdef CONFIG_MODULES
static int
__ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long entry, ptr, tramp;
unsigned long ip = rec->ip;
ppc_inst_t op, pop;

/* read where this goes */
if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {
pr_err("Fetching opcode failed.\n");
return -EFAULT;
}

/* Make sure that this is still a 24bit jump */
if (!is_bl_op(op)) {
pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
return -EINVAL;
}

/* lets find where the pointer goes */
tramp = find_bl_target(ip, op);

pr_devel("ip:%lx jumps to %lx", ip, tramp);

if (module_trampoline_target(mod, tramp, &ptr)) {
pr_err("Failed to get trampoline target\n");
return -EFAULT;
}

pr_devel("trampoline target %lx", ptr);

entry = ppc_global_function_entry((void *)addr);
/* This should match what was called */
if (ptr != entry) {
pr_err("addr %lx does not match expected %lx\n", ptr, entry);
return -EINVAL;
}

if (IS_ENABLED(CONFIG_MPROFILE_KERNEL)) {
if (copy_inst_from_kernel_nofault(&op, (void *)(ip - 4))) {
pr_err("Fetching instruction at %lx failed.\n", ip - 4);
return -EFAULT;
}

/* We expect either a mflr r0, or a std r0, LRSAVE(r1) */
if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_MFLR(_R0))) &&
!ppc_inst_equal(op, ppc_inst(PPC_INST_STD_LR))) {
pr_err("Unexpected instruction %08lx around bl _mcount\n",
ppc_inst_as_ulong(op));
return -EINVAL;
}
} else if (IS_ENABLED(CONFIG_PPC64)) {
/*
* Check what is in the next instruction. We can see ld r2,40(r1), but
* on first pass after boot we will see mflr r0.
*/
if (copy_inst_from_kernel_nofault(&op, (void *)(ip + 4))) {
pr_err("Fetching op failed.\n");
return -EFAULT;
}

if (!ppc_inst_equal(op, ppc_inst(PPC_INST_LD_TOC))) {
pr_err("Expected %08lx found %08lx\n", PPC_INST_LD_TOC,
ppc_inst_as_ulong(op));
return -EINVAL;
}
}

/*
* When using -mprofile-kernel or PPC32 there is no load to jump over.
*
* Otherwise our original call site looks like:
*
* bl <tramp>
* ld r2,XX(r1)
*
* Milton Miller pointed out that we can not simply nop the branch.
* If a task was preempted when calling a trace function, the nops
* will remove the way to restore the TOC in r2 and the r2 TOC will
* get corrupted.
*
* Use a b +8 to jump over the load.
* XXX: could make PCREL depend on MPROFILE_KERNEL
* XXX: check PCREL && MPROFILE_KERNEL calling sequence
*/
if (IS_ENABLED(CONFIG_MPROFILE_KERNEL) || IS_ENABLED(CONFIG_PPC32))
pop = ppc_inst(PPC_RAW_NOP());
else
pop = ppc_inst(PPC_RAW_BRANCH(8)); /* b +8 */

if (patch_instruction((u32 *)ip, pop)) {
pr_err("Patching NOP failed.\n");
return -EPERM;
}

return 0;
}
#else
static int __ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
{
return 0;
}
#endif /* CONFIG_MODULES */

static unsigned long find_ftrace_tramp(unsigned long ip)
{
int i;
Expand All @@ -235,88 +129,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip)
return 0;
}

static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long tramp, ip = rec->ip;
ppc_inst_t op;

/* Read where this goes */
if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {
pr_err("Fetching opcode failed.\n");
return -EFAULT;
}

/* Make sure that this is still a 24bit jump */
if (!is_bl_op(op)) {
pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
return -EINVAL;
}

/* Let's find where the pointer goes */
tramp = find_bl_target(ip, op);

pr_devel("ip:%lx jumps to %lx", ip, tramp);

/* Are ftrace trampolines reachable? */
if (!find_ftrace_tramp(ip)) {
pr_err("No ftrace trampolines reachable from %ps\n", (void *)ip);
return -EINVAL;
}

if (patch_instruction((u32 *)ip, ppc_inst(PPC_RAW_NOP()))) {
pr_err("Patching NOP failed.\n");
return -EPERM;
}

return 0;
}

int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long ip = rec->ip;
ppc_inst_t old, new;

/*
* If the calling address is more that 24 bits away,
* then we had to use a trampoline to make the call.
* Otherwise just update the call site.
*/
if (test_24bit_addr(ip, addr)) {
/* within range */
old = ftrace_call_replace(ip, addr, 1);
new = ppc_inst(PPC_RAW_NOP());
return ftrace_modify_code(ip, old, new);
} else if (core_kernel_text(ip)) {
return __ftrace_make_nop_kernel(rec, addr);
} else if (!IS_ENABLED(CONFIG_MODULES)) {
return -EINVAL;
}

/*
* Out of range jumps are called from modules.
* We should either already have a pointer to the module
* or it has been passed in.
*/
if (!rec->arch.mod) {
if (!mod) {
pr_err("No module loaded addr=%lx\n", addr);
return -EFAULT;
}
rec->arch.mod = mod;
} else if (mod) {
if (mod != rec->arch.mod) {
pr_err("Record mod %p not equal to passed in mod %p\n",
rec->arch.mod, mod);
return -EINVAL;
}
/* nothing to do if mod == rec->arch.mod */
} else
mod = rec->arch.mod;

return __ftrace_make_nop(mod, rec, addr);
}

#ifdef CONFIG_MODULES
/*
* Examine the existing instructions for __ftrace_make_call.
Expand Down Expand Up @@ -607,6 +419,38 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
}
#endif

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long tramp, ip = rec->ip;
ppc_inst_t old, new;

/* Nop-out the ftrace location */
new = ppc_inst(PPC_RAW_NOP());
if (is_offset_in_branch_range(addr - ip)) {
/* Within range */
old = ftrace_create_branch_inst(ip, addr, 1);
return ftrace_modify_code(ip, old, new);
} else if (core_kernel_text(ip)) {
/* We would be branching to one of our ftrace tramps */
tramp = find_ftrace_tramp(ip);
if (!tramp) {
pr_err("0x%lx: No ftrace trampolines reachable\n", ip);
return -EINVAL;
}
old = ftrace_create_branch_inst(ip, tramp, 1);
return ftrace_modify_code(ip, old, new);
} else if (IS_ENABLED(CONFIG_MODULES)) {
/* Module code would be going to one of the module stubs */
if (!mod)
mod = rec->arch.mod;
tramp = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp : mod->arch.tramp_regs);
old = ftrace_create_branch_inst(ip, tramp, 1);
return ftrace_modify_code(ip, old, new);
}

return -EINVAL;
}

int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
unsigned long addr, ip = rec->ip;
Expand Down

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