* [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE
@ 2020-02-17 14:09 Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 1/2] ARM: PLT: Move struct plt_entries definition to header Alexander X Sverdlin
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Alexander X Sverdlin @ 2020-02-17 14:09 UTC (permalink / raw)
To: linux-arm-kernel
Cc: Alexander Sverdlin, linux-kernel, Russell King, Steven Rostedt,
Ingo Molnar, Ard Biesheuvel
From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
FTRACE's function tracer currently doesn't always work on ARM with
MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
code modifier cannot cope with introduced veneers and turns the
function tracer off globally.
ARM64 already has a solution for the problem, refer to the following
patches:
arm64: ftrace: emit ftrace-mod.o contents through code
arm64: module-plts: factor out PLT generation code for ftrace
arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
arm64: ftrace: fix building without CONFIG_MODULES
arm64: ftrace: add support for far branches to dynamic ftrace
arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
But the presented ARM variant has just a half of the footprint in terms of
the changed LoCs. It also retains the code validation-before-modification
instead of switching it off.
Changelog:
v6:
* rebased
v5:
* BUILD_BUG_ON() ensures fixed_plts[] always fits one PLT block
* use "for" loop instead of "while"
* scripts/recordmcount is filtering reloc types
v4:
* Fixed build without CONFIG_FUNCTION_TRACER
* Reorganized pre-allocated PLTs handling in get_module_plt(),
now compiler eliminates the whole FTRACE-related handling code
if ARRAY_SIZE(fixed_plts) == 0
v3:
* Only extend struct dyn_arch_ftrace when ARM_MODULE_PLTS is enabled
v2:
* As suggested by Steven Rostedt, refrain from tree-wide API modification,
save module pointer in struct dyn_arch_ftrace instead (PowerPC way)
Alexander Sverdlin (2):
ARM: PLT: Move struct plt_entries definition to header
ARM: ftrace: Add MODULE_PLTS support
arch/arm/include/asm/ftrace.h | 3 +++
arch/arm/include/asm/module.h | 10 +++++++++
arch/arm/kernel/ftrace.c | 46 ++++++++++++++++++++++++++++++++++++++--
arch/arm/kernel/module-plts.c | 49 +++++++++++++++++++++++++++++++++----------
4 files changed, 95 insertions(+), 13 deletions(-)
--
2.4.6
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v6 1/2] ARM: PLT: Move struct plt_entries definition to header
2020-02-17 14:09 [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Alexander X Sverdlin
@ 2020-02-17 14:09 ` Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 2/2] ARM: ftrace: Add MODULE_PLTS support Alexander X Sverdlin
2021-01-27 4:48 ` [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Florian Fainelli
2 siblings, 0 replies; 5+ messages in thread
From: Alexander X Sverdlin @ 2020-02-17 14:09 UTC (permalink / raw)
To: linux-arm-kernel
Cc: Alexander Sverdlin, linux-kernel, Russell King, Steven Rostedt,
Ingo Molnar, Ard Biesheuvel
From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
No functional change, later it will be re-used in several files.
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
---
arch/arm/include/asm/module.h | 9 +++++++++
arch/arm/kernel/module-plts.c | 9 ---------
2 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 182163b..78e4c16 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -19,6 +19,15 @@ enum {
};
#endif
+#define PLT_ENT_STRIDE L1_CACHE_BYTES
+#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
+#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
+
+struct plt_entries {
+ u32 ldr[PLT_ENT_COUNT];
+ u32 lit[PLT_ENT_COUNT];
+};
+
struct mod_plt_sec {
struct elf32_shdr *plt;
int plt_count;
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index 6e626ab..d330e9e 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -12,10 +12,6 @@
#include <asm/cache.h>
#include <asm/opcodes.h>
-#define PLT_ENT_STRIDE L1_CACHE_BYTES
-#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
-#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
-
#ifdef CONFIG_THUMB2_KERNEL
#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
(PLT_ENT_STRIDE - 4))
@@ -24,11 +20,6 @@
(PLT_ENT_STRIDE - 8))
#endif
-struct plt_entries {
- u32 ldr[PLT_ENT_COUNT];
- u32 lit[PLT_ENT_COUNT];
-};
-
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
--
2.4.6
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v6 2/2] ARM: ftrace: Add MODULE_PLTS support
2020-02-17 14:09 [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 1/2] ARM: PLT: Move struct plt_entries definition to header Alexander X Sverdlin
@ 2020-02-17 14:09 ` Alexander X Sverdlin
2021-01-27 4:48 ` [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Florian Fainelli
2 siblings, 0 replies; 5+ messages in thread
From: Alexander X Sverdlin @ 2020-02-17 14:09 UTC (permalink / raw)
To: linux-arm-kernel
Cc: Alexander Sverdlin, linux-kernel, Russell King, Steven Rostedt,
Ingo Molnar, Ard Biesheuvel
From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
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>
---
arch/arm/include/asm/ftrace.h | 3 +++
arch/arm/include/asm/module.h | 1 +
arch/arm/kernel/ftrace.c | 46 +++++++++++++++++++++++++++++++++++++++++--
arch/arm/kernel/module-plts.c | 44 +++++++++++++++++++++++++++++++++++++----
4 files changed, 88 insertions(+), 6 deletions(-)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 48ec1d0..a4dbac0 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -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)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 78e4c16..961fedb 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -30,6 +30,7 @@ struct plt_entries {
struct mod_plt_sec {
struct elf32_shdr *plt;
+ struct plt_entries *plt_ent;
int plt_count;
};
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 10499d4..75830e5 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -70,6 +70,19 @@ int ftrace_arch_code_modify_post_process(void)
static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
+ s32 offset = addr - pc;
+ s32 blim = 0xfe000008;
+ s32 flim = 0x02000004;
+
+ if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
+ blim = 0xff000004;
+ flim = 0x01000002;
+ }
+
+ if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
+ (offset < blim || offset > flim))
+ return 0;
+
return arm_gen_branch_link(pc, addr);
}
@@ -123,10 +136,22 @@ 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);
old = ftrace_nop_replace(rec);
- new = ftrace_call_replace(ip, adjust_address(rec, addr));
+ new = ftrace_call_replace(ip, aaddr);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!new) {
+ struct module *mod = rec->arch.mod;
+
+ if (mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ new = ftrace_call_replace(ip, aaddr);
+ }
+ }
+#endif
return ftrace_modify_code(rec->ip, old, new, true);
}
@@ -151,12 +176,29 @@ 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);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!old && mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ old = ftrace_call_replace(ip, aaddr);
+ }
+#endif
+
new = ftrace_nop_replace(rec);
ret = ftrace_modify_code(ip, old, new, true);
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index d330e9e..a0524ad 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -4,6 +4,7 @@
*/
#include <linux/elf.h>
+#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
@@ -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.
@@ -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;
@@ -236,6 +270,7 @@ 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;
@@ -243,6 +278,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
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);
--
2.4.6
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE
2020-02-17 14:09 [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 1/2] ARM: PLT: Move struct plt_entries definition to header Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 2/2] ARM: ftrace: Add MODULE_PLTS support Alexander X Sverdlin
@ 2021-01-27 4:48 ` Florian Fainelli
2021-01-27 10:43 ` Alexander Sverdlin
2 siblings, 1 reply; 5+ messages in thread
From: Florian Fainelli @ 2021-01-27 4:48 UTC (permalink / raw)
To: Alexander X Sverdlin, linux-arm-kernel
Cc: Ard Biesheuvel, linux-kernel, Steven Rostedt, Russell King, Ingo Molnar
Hi Alexander,
On 2/17/2020 6:09 AM, Alexander X Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
>
> FTRACE's function tracer currently doesn't always work on ARM with
> MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
> code modifier cannot cope with introduced veneers and turns the
> function tracer off globally.
>
> ARM64 already has a solution for the problem, refer to the following
> patches:
>
> arm64: ftrace: emit ftrace-mod.o contents through code
> arm64: module-plts: factor out PLT generation code for ftrace
> arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
> arm64: ftrace: fix building without CONFIG_MODULES
> arm64: ftrace: add support for far branches to dynamic ftrace
> arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
>
> But the presented ARM variant has just a half of the footprint in terms of
> the changed LoCs. It also retains the code validation-before-modification
> instead of switching it off.
We have been using those patches and I was wondering what happened after
this version since they did not show up upstream nor in Russell's patch
tracker? Would you be willing to resubmit them?
Thanks!
--
Florian
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE
2021-01-27 4:48 ` [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Florian Fainelli
@ 2021-01-27 10:43 ` Alexander Sverdlin
0 siblings, 0 replies; 5+ messages in thread
From: Alexander Sverdlin @ 2021-01-27 10:43 UTC (permalink / raw)
To: Florian Fainelli, linux-arm-kernel
Cc: Ard Biesheuvel, linux-kernel, Steven Rostedt, Russell King, Ingo Molnar
Hello Florian,
On 27/01/2021 05:48, Florian Fainelli wrote:
>> FTRACE's function tracer currently doesn't always work on ARM with
>> MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
>> code modifier cannot cope with introduced veneers and turns the
>> function tracer off globally.
>>
>> ARM64 already has a solution for the problem, refer to the following
>> patches:
>>
>> arm64: ftrace: emit ftrace-mod.o contents through code
>> arm64: module-plts: factor out PLT generation code for ftrace
>> arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
>> arm64: ftrace: fix building without CONFIG_MODULES
>> arm64: ftrace: add support for far branches to dynamic ftrace
>> arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
>>
>> But the presented ARM variant has just a half of the footprint in terms of
>> the changed LoCs. It also retains the code validation-before-modification
>> instead of switching it off.
> We have been using those patches and I was wondering what happened after
> this version since they did not show up upstream nor in Russell's patch
> tracker? Would you be willing to resubmit them?
it's a pity, but nobody ever showed any interest to take them to fix real problem
in FTRACE. A grain of salt would be to remind, that no-one also replied that
the series helped him or a Tested-by: tag. This would probably wake more
interest from maintainers side.
Of course I can re-send them because I personally re-base them regularly.
--
Best regards,
Alexander Sverdlin.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-01-27 10:47 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-17 14:09 [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 1/2] ARM: PLT: Move struct plt_entries definition to header Alexander X Sverdlin
2020-02-17 14:09 ` [PATCH v6 2/2] ARM: ftrace: Add MODULE_PLTS support Alexander X Sverdlin
2021-01-27 4:48 ` [PATCH v6 0/2] ARM: Implement MODULE_PLT support in FTRACE Florian Fainelli
2021-01-27 10:43 ` Alexander Sverdlin
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).