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Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages

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  Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-14 09:50 +0200
    Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-14 10:10 +0200
      Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-14 10:40 +0200
        Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-14 11:30 +0200
          Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-14 11:50 +0200
            RE: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages "Luck, Tony" <tony.luck@intel.com> - 2017-09-14 18:10 +0200
              Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-18 09:10 +0200

#1732086 — Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages

On (09/08/17 20:28), Helge Deller wrote:
[..]
> I don't like this kind of trying to figure out at runtime at all.
> It's too much guessing in here IMHO.

well, may be we can avoid any guessing by checking that the
pointer belongs to .opd section.

for kernel we can add 2 new unsigned longs - __opd_start __opd_end -- and
tweak the corresponding arch/${FOO}/kernel/vmlinux.lds.S file to set those
two, the same way text, unwinding, etc. are set.

.... wait a second.

arch/ia64/kernel/vmlinux.lds.S  already handles .opd section

	.opd : AT(ADDR(.opd) - LOAD_OFFSET) {
		*(.opd)
	}

it just doesn't save start/end addresses. so all we need to to
is

        .opd : AT(ADDR(.opd) - LOAD_OFFSET) {
+               __opd_start = .;
                *(.opd)
+               __opd_end = .;
        }

and tweak symbol dereference

 static inline void *dereference_function_descriptor(void *ptr)
 {
        struct fdesc *desc = ptr;
        void *p;
 
+       if (prt < (void *)__start_opd || (void *)__end_opd < ptr)
+               return ptr;
+
        if (!probe_kernel_address(&desc->ip, p))
                ptr = p;
        return ptr;



now, the modules.

module_frob_arch_sections() has the following lines

	else if (strcmp(".opd", secstrings + s->sh_name) == 0)
		mod->arch.opd = s;

so, once, again, we keep the .opd section info in memory. and we
also have the size of that section

	mod->arch.opd->sh_size = fdescs * sizeof(struct fdesc);

so it seems that we've got what we need. need to provide arch callback
(same way as we do with dereference_function_descriptor() to properly
dereference modules' symbols).


so I think we almost have what we need to make ps/pS smart enough
on ppc64/ia64/parisc.

powerpc and parisc handle kernel .opd section as well:

arch/powerpc/kernel/vmlinux.lds.S:      .opd
arch/parisc/kernel/vmlinux.lds.S:       .opd


need to check more.


> What about this idea:
> For %pF we always have pointers to functions, e.g.: 
>         printk("Going to call: %pF\n", gettimeofday);
>         printk("Going to call: %pF\n", p->func);
> 
> and for %pS most (if not all) usages use some kind of casting 
> from "unsigned long" to "void *", e.g.:
>         printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
>         printk("%s: called from %pS\n", __func__, (void *)__builtin_return_address(0));
>         printk("Faulted at %pS\n", (void *)regs->ip);
> 
> So, what if we for the %pS case simply take the type as it is 
> (unsigned long) and introduce a new printk-format, e.g. "%luS" ?
> The %pS examples above then become:
>         printk("%s: called from %luS\n", __func__, _RET_IP_);
>         printk("%s: called from %luS\n", __func__, __builtin_return_address(0));
>         printk("Faulted at %luS\n", regs->ip);
> 
> That way we don't need type-casting, gain compile-time type 
> checks from the compiler, and we could add a checkpatch (or occinelle)
> check which checks for the combination of %pF/%pS and "void*" keyword
> and suggest to use %luS.
> 
> Opinions?

hm. sounds interesting. but I'm afraid people won't be so happy
to learn a new printk format specifier.

	-ss

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#1732102

On (09/14/17 16:40), Sergey Senozhatsky wrote:
[..]
> powerpc and parisc handle kernel .opd section as well:
> 
> arch/powerpc/kernel/vmlinux.lds.S:      .opd
> arch/parisc/kernel/vmlinux.lds.S:       .opd

for modules, arch-s define mod_arch_specific struct.

parisc has .opd

(fdesc offset should be the start of .opd,
 fdesc_offset + sizeof(fdesc) * fdesc_count should be the .opd address range)

struct mod_arch_specific
{
        unsigned long got_offset, got_count, got_max;
        unsigned long fdesc_offset, fdesc_count, fdesc_max;
        struct {
                unsigned long stub_offset;
                unsigned int stub_entries;
                } *section;
        int unwind_section;
        struct unwind_table *unwind;
};


ia64 has .opd

struct mod_arch_specific {
        struct elf64_shdr *core_plt;    /* core PLT section */
        struct elf64_shdr *init_plt;    /* init PLT section */
        struct elf64_shdr *got;         /* global offset table */
        struct elf64_shdr *opd;         /* official procedure descriptors */
        struct elf64_shdr *unwind;      /* unwind-table section */
        unsigned long gp;               /* global-pointer for module */

        void *core_unw_table;           /* core unwind-table cookie returned by unwinder */
        void *init_unw_table;           /* init unwind-table cookie returned by unwinder */
        unsigned int next_got_entry;    /* index of next available got entry */
};


powerpc does not keep track of .opd, need to add

struct mod_arch_specific {
#ifdef __powerpc64__
        unsigned int stubs_section;     /* Index of stubs section in module */
        unsigned int toc_section;       /* What section is the TOC? */
        bool toc_fixed;                 /* Have we fixed up .TOC.? */
#ifdef CONFIG_DYNAMIC_FTRACE
        unsigned long toc;
        unsigned long tramp;
#endif

#else /* powerpc64 */
        /* Indices of PLT sections within module. */
        unsigned int core_plt_section;
        unsigned int init_plt_section;
#ifdef CONFIG_DYNAMIC_FTRACE
        unsigned long tramp;
#endif
#endif /* powerpc64 */

        /* List of BUG addresses, source line numbers and filenames */
        struct list_head bug_list;
        struct bug_entry *bug_table;
        unsigned int num_bugs;
};


seems like we are looking at a solution here.

thoughts?

	-ss

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#1732113

On 14.09.2017 10:03, Sergey Senozhatsky wrote:
> On (09/14/17 16:40), Sergey Senozhatsky wrote:
> [..]
>> powerpc and parisc handle kernel .opd section as well:
>>
>> arch/powerpc/kernel/vmlinux.lds.S:      .opd
>> arch/parisc/kernel/vmlinux.lds.S:       .opd
> 
> for modules, arch-s define mod_arch_specific struct.
> 
> parisc has .opd
> 
> (fdesc offset should be the start of .opd,
>   fdesc_offset + sizeof(fdesc) * fdesc_count should be the .opd address range)
> 
> struct mod_arch_specific
> {
>          unsigned long got_offset, got_count, got_max;
>          unsigned long fdesc_offset, fdesc_count, fdesc_max;
>          struct {
>                  unsigned long stub_offset;
>                  unsigned int stub_entries;
>                  } *section;
>          int unwind_section;
>          struct unwind_table *unwind;
> };
> 
> 
> ia64 has .opd
> 
> struct mod_arch_specific {
>          struct elf64_shdr *core_plt;    /* core PLT section */
>          struct elf64_shdr *init_plt;    /* init PLT section */
>          struct elf64_shdr *got;         /* global offset table */
>          struct elf64_shdr *opd;         /* official procedure descriptors */
>          struct elf64_shdr *unwind;      /* unwind-table section */
>          unsigned long gp;               /* global-pointer for module */
> 
>          void *core_unw_table;           /* core unwind-table cookie returned by unwinder */
>          void *init_unw_table;           /* init unwind-table cookie returned by unwinder */
>          unsigned int next_got_entry;    /* index of next available got entry */
> };
> 
> 
> powerpc does not keep track of .opd, need to add
> 
> struct mod_arch_specific {
> #ifdef __powerpc64__
>          unsigned int stubs_section;     /* Index of stubs section in module */
>          unsigned int toc_section;       /* What section is the TOC? */
>          bool toc_fixed;                 /* Have we fixed up .TOC.? */
> #ifdef CONFIG_DYNAMIC_FTRACE
>          unsigned long toc;
>          unsigned long tramp;
> #endif
> 
> #else /* powerpc64 */
>          /* Indices of PLT sections within module. */
>          unsigned int core_plt_section;
>          unsigned int init_plt_section;
> #ifdef CONFIG_DYNAMIC_FTRACE
>          unsigned long tramp;
> #endif
> #endif /* powerpc64 */
> 
>          /* List of BUG addresses, source line numbers and filenames */
>          struct list_head bug_list;
>          struct bug_entry *bug_table;
>          unsigned int num_bugs;
> };
> 
> 
> seems like we are looking at a solution here.
> 
> thoughts?

The basic concept of your proposal may work, and since it will avoid such
coding issues in the future I think it's probably the best solution.

Will you come up with a patch ? (I won't have time the next few days).
If yes,I'd be happy to test it on parisc.

Helge

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#1732139

On (09/14/17 10:39), Helge Deller wrote:
[..]
> The basic concept of your proposal may work, and since it will avoid such
> coding issues in the future I think it's probably the best solution.
> 
> Will you come up with a patch ? (I won't have time the next few days).
> If yes,I'd be happy to test it on parisc.

cool.

I think I can try to come up with something. I don't have any access
to affected H/W, so if I won't be able to bring up qemu images I'll
be happy to just hand it over to platform maintainers: arch-s like
parisc64 are way to exotic ;)  my aim is a removal of %pf/%pF here.

let's hear from ia64 and ppc64 guys.

	-ss

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#1732145

On 14.09.2017 11:27, Sergey Senozhatsky wrote:
> On (09/14/17 10:39), Helge Deller wrote:
> [..]
>> The basic concept of your proposal may work, and since it will avoid such
>> coding issues in the future I think it's probably the best solution.
>>
>> Will you come up with a patch ? (I won't have time the next few days).
>> If yes,I'd be happy to test it on parisc.
> 
> cool.
> 
> I think I can try to come up with something. I don't have any access
> to affected H/W, so if I won't be able to bring up qemu images 
There is no qemu for parisc yet, but cross-compiling the kernel on Fedora or
Debian from x86_64 is easy and ready-to-go.
Otherwise it's not a problem, I can try in a few days.

> I'll be happy to just hand it over to platform maintainers: arch-s like
> parisc64 are way to exotic ;)  my aim is a removal of %pf/%pF here.
> 
> let's hear from ia64 and ppc64 guys.

Ok too.

Helge

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#1732408

> let's hear from ia64 and ppc64 guys.

If you write a patch, I can try it on some ia64 h/w.

Please include some test cases (perhaps as a second patch that adds a few good/bad %pF and %pS
to some code (both in base kernel, and in a module).

-Tony

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#1733687

On (09/14/17 16:01), Luck, Tony wrote:
> 
> > let's hear from ia64 and ppc64 guys.
> 
> If you write a patch, I can try it on some ia64 h/w.
> 
> Please include some test cases (perhaps as a second patch that adds a few good/bad %pF and %pS
> to some code (both in base kernel, and in a module).

Hello,

I sent out an RFC patch set.


would the following test case work for you?

kernel)

   echo 1 > /proc/sys/vm/drop_caches

module)

   modprobe zram
   echo 100M > /sys/block/zram0/disksize


---

 drivers/block/zram/zram_drv.c | 15 +++++++++++++++
 fs/drop_caches.c              | 11 +++++++++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 2981c27d3aae..ac92aaeaced0 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1508,6 +1508,12 @@ static int zram_add(void)
 	struct request_queue *queue;
 	int ret, device_id;
 
+	printk("printk#13 %pF\n", (void *)_RET_IP_);
+	printk("printk#14 %pS\n", (void *)_RET_IP_);
+
+	printk("printk#15 %pF\n", __builtin_return_address(0));
+	printk("printk#16 %pS\n", __builtin_return_address(0));
+
 	zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
 	if (!zram)
 		return -ENOMEM;
@@ -1730,6 +1736,15 @@ static int __init zram_init(void)
 {
 	int ret;
 
+	printk("printk#7 %pF\n", zram_init);
+	printk("printk#8 %pS\n", zram_init);
+
+	printk("printk#9 %pF\n", (void *)_RET_IP_);
+	printk("printk#10 %pS\n", (void *)_RET_IP_);
+
+	printk("printk#11 %pF\n", __builtin_return_address(0));
+	printk("printk#12 %pS\n", __builtin_return_address(0));
+
 	ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
 				      zcomp_cpu_up_prepare, zcomp_cpu_dead);
 	if (ret < 0)
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index d72d52b90433..3db4adcac78d 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -39,11 +39,22 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 	iput(toput_inode);
 }
 
+#include <linux/sched.h>
+
 int drop_caches_sysctl_handler(struct ctl_table *table, int write,
 	void __user *buffer, size_t *length, loff_t *ppos)
 {
 	int ret;
 
+	printk("printk#1 %pF\n", schedule_timeout);
+	printk("printk#2 %pS\n", schedule_timeout);
+
+	printk("printk#3 %pF\n", (void *)_RET_IP_);
+	printk("printk#4 %pS\n", (void *)_RET_IP_);
+
+	printk("printk#5 %pF\n", __builtin_return_address(0));
+	printk("printk#6 %pS\n", __builtin_return_address(0));
+
 	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
 	if (ret)
 		return ret;
 

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