Re: [PATCH v2 4/4] kprobes: Remove core dependency on modules

From: Google
Date: Thu Apr 04 2024 - 23:13:22 EST

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On Thu, 4 Apr 2024 17:47:07 +0100
Mark Rutland <mark.rutland@xxxxxxx> wrote:

> On Fri, Apr 05, 2024 at 01:10:26AM +0900, Masami Hiramatsu wrote:
> > On Thu, 04 Apr 2024 18:18:21 +0300
> > "Jarkko Sakkinen" <jarkko@xxxxxxxxxx> wrote:
> >
> > > On Thu Apr 4, 2024 at 11:15 AM EEST, Jarkko Sakkinen wrote:
> > > > On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote:
> > > > > From: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> > > > >
> > > > > Tracing with kprobes while running a monolithic kernel is currently
> > > > > impossible because KPROBES depends on MODULES. While this dependency is
> > > > > necessary when HAVE_KPROBES_ALLOC=n and the core kprobes code allocates
> > > > > memory using module_alloc(), all the other module-specific code only
> > > > > exist to handle the case when MODULES=y, and can be hidden behind
> > > > > ifdeffery.
> > > > >
> > > > > Add the necessary ifdeffery, and remove the dependency on MODULES=y when
> > > > > HAVE_KPROBES_ALLOC=y.
> > > > >
> > > > > As of this patch kprobes can be used when MODULES=n on arm64 and
> > > > > riscv. All other architectures still depend on MODULES, either by virtue
> > > > > of the core dependency on MODULES when HAVE_KPROBES_ALLOC=n, or by
> > > > > virtue of an explciit dependency on MODULES in arch code.
> > > > >
> > > > > Other architectures can enable support by implementing their own
> > > > > kprobes_alloc_insn_page() and kprobes_free_insn_page() which do not
> > > > > depend on MODULES.
> > > > >
> > > > > Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> > > > > Link: https://lore.kernel.org/lkml/20240326134616.7691-1-jarkko@xxxxxxxxxx/
> > > > > [Mark: Remove execmem changes, depend on HAVE_KPROBES_ALLOC]
> > > > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> > > > > Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> > > > > Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
> > > > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > > > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > > > > Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> > > > > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > > > > Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
> > > > > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> > > > > Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> > > > > Cc: Will Deacon <will@xxxxxxxxxx>
> > > > > ---
> > > > > arch/Kconfig | 2 +-
> > > > > kernel/kprobes.c | 46 ++++++++++++++++++++++---------------
> > > > > kernel/trace/trace_kprobe.c | 15 ++++++++++--
> > > > > 3 files changed, 41 insertions(+), 22 deletions(-)
> > > > >
> > > > > diff --git a/arch/Kconfig b/arch/Kconfig
> > > > > index 85bb59f7b8c07..0df2c88547b3c 100644
> > > > > --- a/arch/Kconfig
> > > > > +++ b/arch/Kconfig
> > > > > @@ -52,7 +52,7 @@ config GENERIC_ENTRY
> > > > >
> > > > > config KPROBES
> > > > > bool "Kprobes"
> > > > > - depends on MODULES
> > > > > + depends on MODULES || HAVE_KPROBES_ALLOC
> > > > > depends on HAVE_KPROBES
> > > > > select KALLSYMS
> > > > > select TASKS_RCU if PREEMPTION
> > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > > > > index fa2ee4e59eca2..ec4493a41b505 100644
> > > > > --- a/kernel/kprobes.c
> > > > > +++ b/kernel/kprobes.c
> > > > > @@ -1594,6 +1594,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> > > > > goto out;
> > > > > }
> > > > >
> > > > > +#ifdef CONFIG_MODULES
> > > > > /*
> > > > > * If the module freed '.init.text', we couldn't insert
> > > > > * kprobes in there.
> > > > > @@ -1604,7 +1605,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
> > > > > *probed_mod = NULL;
> > > > > ret = -ENOENT;
> > > > > }
> > > > > +#endif /* CONFIG_MODULES */
> > > > > }
> > > > > +
> > > > > out:
> > > > > preempt_enable();
> > > > > jump_label_unlock();
> > > > > @@ -2484,24 +2487,6 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> > > > > return 0;
> > > > > }
> > > > >
> > > > > -/* Remove all symbols in given area from kprobe blacklist */
> > > > > -static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> > > > > -{
> > > > > - struct kprobe_blacklist_entry *ent, *n;
> > > > > -
> > > > > - list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> > > > > - if (ent->start_addr < start || ent->start_addr >= end)
> > > > > - continue;
> > > > > - list_del(&ent->list);
> > > > > - kfree(ent);
> > > > > - }
> > > > > -}
> > > > > -
> > > > > -static void kprobe_remove_ksym_blacklist(unsigned long entry)
> > > > > -{
> > > > > - kprobe_remove_area_blacklist(entry, entry + 1);
> > > > > -}
> > > > > -
> > > > > int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> > > > > char *type, char *sym)
> > > > > {
> > > > > @@ -2566,6 +2551,25 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
> > > > > return ret ? : arch_populate_kprobe_blacklist();
> > > > > }
> > > > >
> > > > > +#ifdef CONFIG_MODULES
> > > > > +/* Remove all symbols in given area from kprobe blacklist */
> > > > > +static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> > > > > +{
> > > > > + struct kprobe_blacklist_entry *ent, *n;
> > > > > +
> > > > > + list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> > > > > + if (ent->start_addr < start || ent->start_addr >= end)
> > > > > + continue;
> > > > > + list_del(&ent->list);
> > > > > + kfree(ent);
> > > > > + }
> > > > > +}
> > > > > +
> > > > > +static void kprobe_remove_ksym_blacklist(unsigned long entry)
> > > > > +{
> > > > > + kprobe_remove_area_blacklist(entry, entry + 1);
> > > > > +}
> > > > > +
> > > > > static void add_module_kprobe_blacklist(struct module *mod)
> > > > > {
> > > > > unsigned long start, end;
> > > > > @@ -2662,6 +2666,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
> > > > > mutex_unlock(&kprobe_mutex);
> > > > > return NOTIFY_DONE;
> > > > > }
> > > > > +#else
> > > > > +#define kprobes_module_callback (NULL)
> > > > > +#endif /* CONFIG_MODULES */
> > > > >
> > > > > static struct notifier_block kprobe_module_nb = {
> > > > > .notifier_call = kprobes_module_callback,
> > > > > @@ -2726,7 +2733,8 @@ static int __init init_kprobes(void)
> > > > > err = arch_init_kprobes();
> > > > > if (!err)
> > > > > err = register_die_notifier(&kprobe_exceptions_nb);
> > > > > - if (!err)
> > > > > +
> > > > > + if (!err && IS_ENABLED(CONFIG_MODULES))
> > > > > err = register_module_notifier(&kprobe_module_nb);
> > > > >
> > > > > kprobes_initialized = (err == 0);
> > > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > > > > index 14099cc17fc9e..c509ba776e679 100644
> > > > > --- a/kernel/trace/trace_kprobe.c
> > > > > +++ b/kernel/trace/trace_kprobe.c
> > > > > @@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> > > > > return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
> > > > > }
> > > > >
> > > > > +#ifdef CONFIG_MODULES
> > > > > static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> > > > > {
> > > > > char *p;
> > > > > @@ -129,6 +130,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> > > > >
> > > > > return ret;
> > > > > }
> > > > > +#else
> > > > > +#define trace_kprobe_module_exist(tk) false /* aka a module never exists */
> > > > > +#endif /* CONFIG_MODULES */
> > > > >
> > > > > static bool trace_kprobe_is_busy(struct dyn_event *ev)
> > > > > {
> > > > > @@ -670,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> > > > > return ret;
> > > > > }
> > > > >
> > > > > +#ifdef CONFIG_MODULES
> > > > > /* Module notifier call back, checking event on the module */
> > > > > static int trace_kprobe_module_callback(struct notifier_block *nb,
> > > > > unsigned long val, void *data)
> > > > > @@ -699,6 +704,9 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
> > > > >
> > > > > return NOTIFY_DONE;
> > > > > }
> > > > > +#else
> > > > > +#define trace_kprobe_module_callback (NULL)
> > > > > +#endif /* CONFIG_MODULES */
> > > > >
> > > > > static struct notifier_block trace_kprobe_module_nb = {
> > > > > .notifier_call = trace_kprobe_module_callback,
> > > > > @@ -1933,8 +1941,11 @@ static __init int init_kprobe_trace_early(void)
> > > > > if (ret)
> > > > > return ret;
> > > > >
> > > > > - if (register_module_notifier(&trace_kprobe_module_nb))
> > > > > - return -EINVAL;
> > > > > + if (IS_ENABLED(CONFIG_MODULES)) {
> > > > > + ret = register_module_notifier(&trace_kprobe_module_nb);
> > > > > + if (ret)
> > > > > + return -EINVAL;
> > > > > + }
> > > > >
> > > > > return 0;
> > > > > }
> > > >
> > > > 2/4, 3/4, 4/4:
> > > >
> > > > Tested-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> # arch/riscv
> > >
> > > Hey, I tried the pci_proc_init example:
> > >
> > > [ 3.060703] ------------[ ftrace bug ]------------
> > > [ 3.060944] ftrace faulted on writing
> > > [ 3.060987] [<ffffffff8102c0da>] pci_proc_init+0x0/0x80
> > > [ 3.061509] Updating ftrace call site to call a different ftrace function
> > > [ 3.061756] ftrace record flags: 80100001
> > > [ 3.061925] (1)
> > > [ 3.061925] expected tramp: ffffffff8000aa60
> > > [ 3.062527] ------------[ cut here ]------------
> > > [ 3.062652] WARNING: CPU: 0 PID: 18 at kernel/trace/ftrace.c:2180 ftrace_bug+0x282/0x2b8
> > > [ 3.062747] CPU: 0 PID: 18 Comm: migration/0 Not tainted 6.9.0-rc1 #2
> > > [ 3.062807] Hardware name: riscv-virtio,qemu (DT)
> > > [ 3.062868] Stopper: multi_cpu_stop+0x0/0x1a0 <- stop_machine_cpuslocked+0x140/0x18c
> > > [ 3.062925] epc : ftrace_bug+0x282/0x2b8
> > > [ 3.062957] ra : ftrace_bug+0x282/0x2b8
> > > [ 3.062989] epc : ffffffff80fc31f4 ra : ffffffff80fc31f4 sp : ff20000000093c70
> > > [ 3.063014] gp : ffffffff824b7780 tp : ff60000002a85940 t0 : ffffffff800923a6
> > > [ 3.063037] t1 : 0000000000000020 t2 : 6465746365707865 s0 : ff20000000093cb0
> > > [ 3.063061] s1 : ffffffff8102c0da a0 : 0000000000000022 a1 : ffffffff8229b7f0
> > > [ 3.063084] a2 : 0000000000000010 a3 : fffffffffffffffe a4 : 0000000000000000
> > > [ 3.063108] a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000001
> > > [ 3.063131] s2 : ff60000002850ab0 s3 : ffffffffffffffff s4 : 0000000000000002
> > > [ 3.063154] s5 : 0000000002000000 s6 : 0000000082000000 s7 : 0000000000000000
> > > [ 3.063178] s8 : 0000000000000001 s9 : ffffffff824bca18 s10: ff60000002845140
> > > [ 3.063202] s11: 00000000000000ab t3 : ffffffff824ce9ef t4 : ffffffff824ce9ef
> > > [ 3.063225] t5 : ffffffff824ce9f0 t6 : ff20000000093aa8
> > > [ 3.063248] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
> > > [ 3.063331] [<ffffffff80fc31f4>] ftrace_bug+0x282/0x2b8
> > > [ 3.063398] [<ffffffff80108b1a>] ftrace_replace_code+0xfe/0x168
> > > [ 3.063430] [<ffffffff80108c82>] ftrace_modify_all_code+0x5c/0x16a
> > > [ 3.063460] [<ffffffff80108da2>] __ftrace_modify_code+0x12/0x1c
> > > [ 3.063490] [<ffffffff800f299c>] multi_cpu_stop+0x118/0x1a0
> > > [ 3.063519] [<ffffffff800f242e>] cpu_stopper_thread+0xb2/0x12a
> > > [ 3.063548] [<ffffffff8005dece>] smpboot_thread_fn+0x1aa/0x1d2
> > > [ 3.063577] [<ffffffff80057fec>] kthread+0xfe/0x106
> > > [ 3.063606] [<ffffffff80fe3d76>] ret_from_fork+0xe/0x20
> > > [ 3.063676] ---[ end trace 0000000000000000 ]---
> > > [ 3.069730] ------------[ cut here ]------------
> > > [ 3.069861] Failed to disarm kprobe-ftrace at pci_proc_init+0x0/0x80 (error -19)
> > > [ 3.070078] WARNING: CPU: 0 PID: 1 at kernel/kprobes.c:1128 __disarm_kprobe_ftrace+0x9a/0xae
> > > [ 3.070124] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.9.0-rc1 #2
> > > [ 3.070133] Hardware name: riscv-virtio,qemu (DT)
> > > [ 3.070141] epc : __disarm_kprobe_ftrace+0x9a/0xae
> > > [ 3.070150] ra : __disarm_kprobe_ftrace+0x9a/0xae
> > > [ 3.070157] epc : ffffffff800ffcda ra : ffffffff800ffcda sp : ff2000000000be30
> > > [ 3.070162] gp : ffffffff824b7780 tp : ff60000002a70000 t0 : ffffffff800923a6
> > > [ 3.070167] t1 : 0000000000000046 t2 : 6f742064656c6961 s0 : ff2000000000be60
> > > [ 3.070173] s1 : ffffffffffffffed a0 : 0000000000000044 a1 : ffffffff8229b7f0
> > > [ 3.070178] a2 : 0000000000000010 a3 : fffffffffffffffe a4 : 0000000000000000
> > > [ 3.070182] a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000001
> > > [ 3.070187] s2 : ffffffff824bc940 s3 : ffffffff822ac158 s4 : ff60000002b53c80
> > > [ 3.070192] s5 : ffffffff824bc940 s6 : ffffffff822ac158 s7 : ffffffff81000000
> > > [ 3.070197] s8 : ffffffff814775f8 s9 : ffffffff824f23d8 s10: 0000000000000000
> > > [ 3.070202] s11: 0000000000000000 t3 : ffffffff824ce9d7 t4 : ffffffff824ce9d7
> > > [ 3.070206] t5 : ffffffff824ce9d8 t6 : ff2000000000bc48
> > > [ 3.070211] status: 0000000200000120 badaddr: 0000000000000000 cause: 0000000000000003
> > > [ 3.070218] [<ffffffff800ffcda>] __disarm_kprobe_ftrace+0x9a/0xae
> > > [ 3.070228] [<ffffffff80101b16>] kprobe_free_init_mem+0xc2/0x130
> > > [ 3.070236] [<ffffffff80fd9b38>] kernel_init+0x46/0x14e
> > > [ 3.070245] [<ffffffff80fe3d76>] ret_from_fork+0xe/0x20
> > > [ 3.070254] ---[ end trace 0000000000000000 ]---
> > > [
> > >
> > > This is with riscv64 defconfig, tracing shenanigans and the following
> > > bootconfig and the bug was realized in QEMU:
> >
> > So this is with CONFIG_MODULES=y?
> > This seems like an actual bug but not related to this series.
> > Can you reproduce this without this patch series?
>
> IIUC what's going on here is:
>
> CONFIG_MODULES=n
>
> . and so CONFIG_STRICT_MODULE_RWX=n
>
> When kprobe_free_init_mem() is called, system_state == SYSTEM_FREEING_INITMEM, which causes
> core_kernel_text() to return 0 for inittext:
>
> | int notrace core_kernel_text(unsigned long addr)
> | {
> | if (is_kernel_text(addr))
> | return 1;
> |
> | if (system_state < SYSTEM_FREEING_INITMEM &&
> | is_kernel_inittext(addr))
> | return 1;
> | return 0;
> | }
>
> This causes riscv's patch_map() to *not* fixmap the inittext, since it does:
>
> | if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr))
> | page = phys_to_page(__pa_symbol(addr));
> | else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
> | page = vmalloc_to_page(addr);
> | else
> | return addr;
>
> .. which fails core_kernel_text(), and IS_ENABLED(CONFIG_STRICT_MODULE_RWX),
> returning the (read-only) mapping of the kernel image.

Ah, I got it. Yes, kprobes is able to probe on init text.
(in the boot time and module load time)

>
> That would happen (by luck) to work with CONFIG_MODULES=because it'd be handled
> by vmalloc_to_page() walking the page tables. I suspect that'll happen to work
> on arm64 by virtue of patch 1, but that wasn't intentional.

Yeah, even with init text, it should be handled as a part of text address.
So using phys_to_page() will be better.

>
> I'm not sure what the right fix is here, it's annoying that core_kernel_text()
> is special-cased for SYSTEM_FREEING_INITMEM, but that was deliberate as of
> commit:
>
> d2635f2012a44e3d ("mm: create a new system state and fix core_kernel_text()")
>
> .. though I'm not sure what exactly that was trying to fix at a higher level.

at the kprobe_free_init_mem() point, init text is not freed yet, so why not we check
the is_kernel_inittext() in patch_map()? I think this special case is handled in
patch_map(). (Or, we can introduce early_patch_map())

>
> I can look into this some more tomorrow.

Thank you!

>
> Mark.
>

--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

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In reply to: Mark Rutland: "Re: [PATCH v2 4/4] kprobes: Remove core dependency on modules"
Next in thread: Mark Rutland: "[PATCH v2 3/4] kprobes/treewide: Explicitly override alloc/free functions"
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