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ARM: 9079/1: ftrace: Add MODULE_PLTS support
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Teach ftrace_make_call() and ftrace_make_nop() about PLTs.
Teach PLT code about FTRACE and all its callbacks.
Otherwise the following might happen:

------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../arch/arm/kernel/insn.c:14 __arm_gen_branch+0x83/0x8c()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c03143cf>] (__arm_gen_branch+0x83/0x8c)
[<c03143cf>] (__arm_gen_branch) from [<c0314337>] (ftrace_make_nop+0xf/0x24)
[<c0314337>] (ftrace_make_nop) from [<c038ebcb>] (ftrace_process_locs+0x27b/0x3e8)
[<c038ebcb>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcc ]---
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1b1/0x234()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c038e87d>] (ftrace_bug+0x1b1/0x234)
[<c038e87d>] (ftrace_bug) from [<c038ebd5>] (ftrace_process_locs+0x285/0x3e8)
[<c038ebd5>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcd ]---
ftrace failed to modify [<e9ef7006>] 0xe9ef7006
actual: 02:f0:3b:fa
ftrace record flags: 0
(0) expected tramp: c0314265

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
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@asverdlin
asverdlin authored and Russell King (Oracle) committed Jun 7, 2021
1 parent 890cb05 commit 79f32b2
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Showing 4 changed files with 82 additions and 12 deletions.
3 changes: 3 additions & 0 deletions arch/arm/include/asm/ftrace.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,9 @@ extern void __gnu_mcount_nc(void);

#ifdef CONFIG_DYNAMIC_FTRACE
struct dyn_arch_ftrace {
#ifdef CONFIG_ARM_MODULE_PLTS
struct module *mod;
#endif
};

static inline unsigned long ftrace_call_adjust(unsigned long addr)
Expand Down
1 change: 1 addition & 0 deletions arch/arm/include/asm/module.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ struct plt_entries {

struct mod_plt_sec {
struct elf32_shdr *plt;
struct plt_entries *plt_ent;
int plt_count;
};

Expand Down
46 changes: 38 additions & 8 deletions arch/arm/kernel/ftrace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -68,9 +68,10 @@ int ftrace_arch_code_modify_post_process(void)
return 0;
}

static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr,
bool warn)
{
return arm_gen_branch_link(pc, addr, true);
return arm_gen_branch_link(pc, addr, warn);
}

static int ftrace_modify_code(unsigned long pc, unsigned long old,
Expand Down Expand Up @@ -104,14 +105,14 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
int ret;

pc = (unsigned long)&ftrace_call;
new = ftrace_call_replace(pc, (unsigned long)func);
new = ftrace_call_replace(pc, (unsigned long)func, true);

ret = ftrace_modify_code(pc, 0, new, false);

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
if (!ret) {
pc = (unsigned long)&ftrace_regs_call;
new = ftrace_call_replace(pc, (unsigned long)func);
new = ftrace_call_replace(pc, (unsigned long)func, true);

ret = ftrace_modify_code(pc, 0, new, false);
}
Expand All @@ -124,10 +125,22 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long new, old;
unsigned long ip = rec->ip;
unsigned long aaddr = adjust_address(rec, addr);
struct module *mod = NULL;

#ifdef CONFIG_ARM_MODULE_PLTS
mod = rec->arch.mod;
#endif

old = ftrace_nop_replace(rec);

new = ftrace_call_replace(ip, adjust_address(rec, addr));
new = ftrace_call_replace(ip, aaddr, !mod);
#ifdef CONFIG_ARM_MODULE_PLTS
if (!new && mod) {
aaddr = get_module_plt(mod, ip, aaddr);
new = ftrace_call_replace(ip, aaddr, true);
}
#endif

return ftrace_modify_code(rec->ip, old, new, true);
}
Expand All @@ -140,9 +153,9 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long new, old;
unsigned long ip = rec->ip;

old = ftrace_call_replace(ip, adjust_address(rec, old_addr));
old = ftrace_call_replace(ip, adjust_address(rec, old_addr), true);

new = ftrace_call_replace(ip, adjust_address(rec, addr));
new = ftrace_call_replace(ip, adjust_address(rec, addr), true);

return ftrace_modify_code(rec->ip, old, new, true);
}
Expand All @@ -152,12 +165,29 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long aaddr = adjust_address(rec, addr);
unsigned long ip = rec->ip;
unsigned long old;
unsigned long new;
int ret;

old = ftrace_call_replace(ip, adjust_address(rec, addr));
#ifdef CONFIG_ARM_MODULE_PLTS
/* mod is only supplied during module loading */
if (!mod)
mod = rec->arch.mod;
else
rec->arch.mod = mod;
#endif

old = ftrace_call_replace(ip, aaddr,
!IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || !mod);
#ifdef CONFIG_ARM_MODULE_PLTS
if (!old && mod) {
aaddr = get_module_plt(mod, ip, aaddr);
old = ftrace_call_replace(ip, aaddr, true);
}
#endif

new = ftrace_nop_replace(rec);
ret = ftrace_modify_code(ip, old, new, true);

Expand Down
44 changes: 40 additions & 4 deletions arch/arm/kernel/module-plts.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
*/

#include <linux/elf.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
Expand All @@ -20,19 +21,52 @@
(PLT_ENT_STRIDE - 8))
#endif

static const u32 fixed_plts[] = {
#ifdef CONFIG_FUNCTION_TRACER
FTRACE_ADDR,
MCOUNT_ADDR,
#endif
};

static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
}

static void prealloc_fixed(struct mod_plt_sec *pltsec, struct plt_entries *plt)
{
int i;

if (!ARRAY_SIZE(fixed_plts) || pltsec->plt_count)
return;
pltsec->plt_count = ARRAY_SIZE(fixed_plts);

for (i = 0; i < ARRAY_SIZE(plt->ldr); ++i)
plt->ldr[i] = PLT_ENT_LDR;

BUILD_BUG_ON(sizeof(fixed_plts) > sizeof(plt->lit));
memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
}

u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
struct plt_entries *plt;
int idx;

/* cache the address, ELF header is available only during module load */
if (!pltsec->plt_ent)
pltsec->plt_ent = (struct plt_entries *)pltsec->plt->sh_addr;
plt = pltsec->plt_ent;

struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
int idx = 0;
prealloc_fixed(pltsec, plt);

for (idx = 0; idx < ARRAY_SIZE(fixed_plts); ++idx)
if (plt->lit[idx] == val)
return (u32)&plt->ldr[idx];

idx = 0;
/*
* Look for an existing entry pointing to 'val'. Given that the
* relocations are sorted, this will be the last entry we allocated.
Expand Down Expand Up @@ -180,8 +214,8 @@ static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
unsigned long core_plts = 0;
unsigned long init_plts = 0;
unsigned long core_plts = ARRAY_SIZE(fixed_plts);
unsigned long init_plts = ARRAY_SIZE(fixed_plts);
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
Elf32_Sym *syms = NULL;

Expand Down Expand Up @@ -236,13 +270,15 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.core.plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
sizeof(struct plt_entries));
mod->arch.core.plt_count = 0;
mod->arch.core.plt_ent = NULL;

mod->arch.init.plt->sh_type = SHT_NOBITS;
mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES;
mod->arch.init.plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
sizeof(struct plt_entries));
mod->arch.init.plt_count = 0;
mod->arch.init.plt_ent = NULL;

pr_debug("%s: plt=%x, init.plt=%x\n", __func__,
mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
Expand Down

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