diff mbox

[3/5] powerpc64: Add .opd based function descriptor dereference

Message ID 20170916035347.19705-4-sergey.senozhatsky@gmail.com (mailing list archive)
State Superseded
Headers show

Commit Message

Sergey Senozhatsky Sept. 16, 2017, 3:53 a.m. UTC
We are moving towards separate kernel and module function descriptor
dereference callbacks. This patch enables it for powerpc64.

For pointers that belong to the kernel
-  Added __start_opd and __end_opd pointers, to track the kernel
   .opd section address range;

-  Added dereference_kernel_function_descriptor(). Now we
   will dereference only function pointers that are within
   [__start_opd, __end_opd];

For pointers that belong to a module
-  Added dereference_module_function_descriptor() to handle module
   function descriptor dereference. Now we will dereference only
   pointers that are within [module->opd.start, module->opd.end].

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 arch/powerpc/include/asm/module.h   |  3 +++
 arch/powerpc/include/asm/sections.h | 13 +++++++++++++
 arch/powerpc/kernel/module_64.c     | 16 ++++++++++++++++
 arch/powerpc/kernel/vmlinux.lds.S   |  2 ++
 4 files changed, 34 insertions(+)

Comments

Naveen N. Rao Sept. 16, 2017, 9:43 a.m. UTC | #1
On 2017/09/16 12:53PM, Sergey Senozhatsky wrote:
> We are moving towards separate kernel and module function descriptor
> dereference callbacks. This patch enables it for powerpc64.
> 
> For pointers that belong to the kernel
> -  Added __start_opd and __end_opd pointers, to track the kernel
>    .opd section address range;
> 
> -  Added dereference_kernel_function_descriptor(). Now we
>    will dereference only function pointers that are within
>    [__start_opd, __end_opd];
> 
> For pointers that belong to a module
> -  Added dereference_module_function_descriptor() to handle module
>    function descriptor dereference. Now we will dereference only
>    pointers that are within [module->opd.start, module->opd.end].

Would it be simpler to just use kernel_text_address() and dereference 
everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only 
dereference function descriptor for non-text symbols") for a related 
patch.

- Naveen

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Sergey Senozhatsky Sept. 16, 2017, 11:25 a.m. UTC | #2
On (09/16/17 15:13), Naveen N. Rao wrote:
[..]
> Would it be simpler to just use kernel_text_address() and dereference 
> everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only 
> dereference function descriptor for non-text symbols") for a related 
> patch.

I had this idea, see

lkml.kernel.org/r/20170908172528.qc2vdtxzqh777k6o@intel.com


	-ss
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Michael Ellerman Sept. 19, 2017, 10:22 a.m. UTC | #3
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:

> On 2017/09/16 12:53PM, Sergey Senozhatsky wrote:
>> We are moving towards separate kernel and module function descriptor
>> dereference callbacks. This patch enables it for powerpc64.
>> 
>> For pointers that belong to the kernel
>> -  Added __start_opd and __end_opd pointers, to track the kernel
>>    .opd section address range;
>> 
>> -  Added dereference_kernel_function_descriptor(). Now we
>>    will dereference only function pointers that are within
>>    [__start_opd, __end_opd];
>> 
>> For pointers that belong to a module
>> -  Added dereference_module_function_descriptor() to handle module
>>    function descriptor dereference. Now we will dereference only
>>    pointers that are within [module->opd.start, module->opd.end].
>
> Would it be simpler to just use kernel_text_address() and dereference 
> everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only 
> dereference function descriptor for non-text symbols") for a related 
> patch.

Yeah that would be a lot simpler and probably work perfectly well.

cheers
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Sergey Senozhatsky Sept. 19, 2017, 10:31 a.m. UTC | #4
On (09/19/17 20:22), Michael Ellerman wrote:
> > On 2017/09/16 12:53PM, Sergey Senozhatsky wrote:
> >> We are moving towards separate kernel and module function descriptor
> >> dereference callbacks. This patch enables it for powerpc64.
> >> 
> >> For pointers that belong to the kernel
> >> -  Added __start_opd and __end_opd pointers, to track the kernel
> >>    .opd section address range;
> >> 
> >> -  Added dereference_kernel_function_descriptor(). Now we
> >>    will dereference only function pointers that are within
> >>    [__start_opd, __end_opd];
> >> 
> >> For pointers that belong to a module
> >> -  Added dereference_module_function_descriptor() to handle module
> >>    function descriptor dereference. Now we will dereference only
> >>    pointers that are within [module->opd.start, module->opd.end].
> >
> > Would it be simpler to just use kernel_text_address() and dereference 
> > everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only 
> > dereference function descriptor for non-text symbols") for a related 
> > patch.
> 
> Yeah that would be a lot simpler and probably work perfectly well.

unlike ppc_function_entry(), printk() can get called on any symbol,
not just function pointers.

for example,

cat /proc/kallsyms | grep shrinker_rwsem
ffffffff81a4b1e0 d shrinker_rwsem

or

cat /proc/kallsyms | grep vm_total_pages
ffffffff81dcd418 B vm_total_pages


and so on.

	-ss
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Michael Ellerman Sept. 20, 2017, 1:51 a.m. UTC | #5
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> writes:

> On (09/19/17 20:22), Michael Ellerman wrote:
>> > On 2017/09/16 12:53PM, Sergey Senozhatsky wrote:
>> >> We are moving towards separate kernel and module function descriptor
>> >> dereference callbacks. This patch enables it for powerpc64.
>> >> 
>> >> For pointers that belong to the kernel
>> >> -  Added __start_opd and __end_opd pointers, to track the kernel
>> >>    .opd section address range;
>> >> 
>> >> -  Added dereference_kernel_function_descriptor(). Now we
>> >>    will dereference only function pointers that are within
>> >>    [__start_opd, __end_opd];
>> >> 
>> >> For pointers that belong to a module
>> >> -  Added dereference_module_function_descriptor() to handle module
>> >>    function descriptor dereference. Now we will dereference only
>> >>    pointers that are within [module->opd.start, module->opd.end].
>> >
>> > Would it be simpler to just use kernel_text_address() and dereference 
>> > everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only 
>> > dereference function descriptor for non-text symbols") for a related 
>> > patch.
>> 
>> Yeah that would be a lot simpler and probably work perfectly well.
>
> unlike ppc_function_entry(), printk() can get called on any symbol,
> not just function pointers.
>
> for example,
>
> cat /proc/kallsyms | grep shrinker_rwsem
> ffffffff81a4b1e0 d shrinker_rwsem

Yep, good point. So your patch is probably good then. Maybe someone
other than me can find time to test it ;)

cheers
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Sergey Senozhatsky Sept. 20, 2017, 6:10 a.m. UTC | #6
On (09/20/17 11:51), Michael Ellerman wrote:
[..]
> > unlike ppc_function_entry(), printk() can get called on any symbol,
> > not just function pointers.
> >
> > for example,
> >
> > cat /proc/kallsyms | grep shrinker_rwsem
> > ffffffff81a4b1e0 d shrinker_rwsem
> 
> Yep, good point. So your patch is probably good then. Maybe someone
> other than me can find time to test it ;)

Hi,

I'll re-spin the series today/tomorrow.

	-ss
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diff mbox

Patch

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 6c0132c7212f..7e28442827f1 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -45,6 +45,9 @@  struct mod_arch_specific {
 	unsigned long tramp;
 #endif
 
+	/* For module function descriptor dereference */
+	unsigned long start_opd;
+	unsigned long end_opd;
 #else /* powerpc64 */
 	/* Indices of PLT sections within module. */
 	unsigned int core_plt_section;
diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index 7902d6358854..7cc4db86952b 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -16,6 +16,9 @@  extern char __end_interrupts[];
 extern char __prom_init_toc_start[];
 extern char __prom_init_toc_end[];
 
+extern char __start_opd[];
+extern char __end_opd[];
+
 static inline int in_kernel_text(unsigned long addr)
 {
 	if (addr >= (unsigned long)_stext && addr < (unsigned long)__init_end)
@@ -66,6 +69,8 @@  static inline int overlaps_kvm_tmp(unsigned long start, unsigned long end)
 
 #ifdef PPC64_ELF_ABI_v1
 #undef dereference_function_descriptor
+#undef dereference_kernel_function_descriptor
+
 static inline void *dereference_function_descriptor(void *ptr)
 {
 	struct ppc64_opd_entry *desc = ptr;
@@ -75,6 +80,14 @@  static inline void *dereference_function_descriptor(void *ptr)
 		ptr = p;
 	return ptr;
 }
+
+static inline void *dereference_kernel_function_descriptor(void *ptr)
+{
+	if (ptr < (void *)__start_opd || (void *)__end_opd < ptr)
+		return ptr;
+
+	return dereference_function_descriptor(ptr);
+}
 #endif /* PPC64_ELF_ABI_v1 */
 
 #endif
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 0b0f89685b67..52aa5d668364 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -344,6 +344,11 @@  int module_frob_arch_sections(Elf64_Ehdr *hdr,
 		else if (strcmp(secstrings+sechdrs[i].sh_name,"__versions")==0)
 			dedotify_versions((void *)hdr + sechdrs[i].sh_offset,
 					  sechdrs[i].sh_size);
+		else if (strcmp(secstrings + sechdrs[i].sh_name, ".opd")==0) {
+			me->arch.start_opd = sechdrs[i].sh_offset;
+			me->arch.end_opd = me->arch.start_opd +
+					sechdrs[i].sh_size;
+		}
 
 		/* We don't handle .init for the moment: rename to _init */
 		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
@@ -712,6 +717,17 @@  int apply_relocate_add(Elf64_Shdr *sechdrs,
 	return 0;
 }
 
+#ifdef PPC64_ELF_ABI_v1
+unsigned long dereference_module_function_descriptor(struct module *mod,
+						     unsigned long addr)
+{
+	if (addr < mod->arch.start_opd || mod->arch.end_opd < addr)
+		return addr;
+
+	return dereference_function_descriptor(addr);
+}
+#endif /* PPC64_ELF_ABI_v1 */
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 #ifdef CC_USING_MPROFILE_KERNEL
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 882628fa6987..70e10251e083 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -277,7 +277,9 @@  SECTIONS
 	}
 
 	.opd : AT(ADDR(.opd) - LOAD_OFFSET) {
+		__start_opd = .;
 		*(.opd)
+		__end_opd = .;
 	}
 
 	. = ALIGN(256);