diff mbox series

[v3,04/12] powerpc: Prepare func_desc_t for refactorisation

Message ID 86c393ce0a6f603f94e6d2ceca08d535f654bb23.1634457599.git.christophe.leroy@csgroup.eu (mailing list archive)
State New
Headers show
Series Fix LKDTM for PPC64/IA64/PARISC | expand

Commit Message

Christophe Leroy Oct. 17, 2021, 12:38 p.m. UTC
In preparation of making func_desc_t generic, change the ELFv2
version to a struct containing 'addr' element.

This allows using single helpers common to ELFv1 and ELFv2.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/module_64.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

Comments

Nicholas Piggin Oct. 18, 2021, 6:27 a.m. UTC | #1
Excerpts from Christophe Leroy's message of October 17, 2021 10:38 pm:
> In preparation of making func_desc_t generic, change the ELFv2
> version to a struct containing 'addr' element.
> 
> This allows using single helpers common to ELFv1 and ELFv2.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
>  arch/powerpc/kernel/module_64.c | 32 ++++++++++++++------------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index a89da0ee25e2..b687ef88c4c4 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -33,19 +33,13 @@
>  #ifdef PPC64_ELF_ABI_v2
>  
>  /* An address is simply the address of the function. */
> -typedef unsigned long func_desc_t;
> +typedef struct {
> +	unsigned long addr;
> +} func_desc_t;

I'm not quite following why this change is done. I guess it is so you 
can move this func_desc_t type into core code, but why do that? Is it
just to avoid using the preprocessor?

On its own this patch looks okay.

Acked-by: Nicholas Piggin <npiggin@gmail.com>
Christophe Leroy Oct. 18, 2021, 7:08 a.m. UTC | #2
Le 18/10/2021 à 08:27, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of October 17, 2021 10:38 pm:
>> In preparation of making func_desc_t generic, change the ELFv2
>> version to a struct containing 'addr' element.
>>
>> This allows using single helpers common to ELFv1 and ELFv2.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> 
>> ---
>>   arch/powerpc/kernel/module_64.c | 32 ++++++++++++++------------------
>>   1 file changed, 14 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
>> index a89da0ee25e2..b687ef88c4c4 100644
>> --- a/arch/powerpc/kernel/module_64.c
>> +++ b/arch/powerpc/kernel/module_64.c
>> @@ -33,19 +33,13 @@
>>   #ifdef PPC64_ELF_ABI_v2
>>   
>>   /* An address is simply the address of the function. */
>> -typedef unsigned long func_desc_t;
>> +typedef struct {
>> +	unsigned long addr;
>> +} func_desc_t;
> 
> I'm not quite following why this change is done. I guess it is so you
> can move this func_desc_t type into core code, but why do that? Is it
> just to avoid using the preprocessor?

I explained it in patch 7 but yes it probably also deserves some more 
explanation here as well.

That's right, it's to avoid having to spread #ifdefs everywhere.

> 
> On its own this patch looks okay.
> 
> Acked-by: Nicholas Piggin <npiggin@gmail.com>
>
Kees Cook Feb. 11, 2022, 12:54 a.m. UTC | #3
On Sun, Oct 17, 2021 at 02:38:17PM +0200, Christophe Leroy wrote:
> In preparation of making func_desc_t generic, change the ELFv2
> version to a struct containing 'addr' element.
> 
> This allows using single helpers common to ELFv1 and ELFv2.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/module_64.c | 32 ++++++++++++++------------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index a89da0ee25e2..b687ef88c4c4 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -33,19 +33,13 @@
>  #ifdef PPC64_ELF_ABI_v2
>  
>  /* An address is simply the address of the function. */
> -typedef unsigned long func_desc_t;
> +typedef struct {
> +	unsigned long addr;
> +} func_desc_t;
>  
>  static func_desc_t func_desc(unsigned long addr)
>  {
> -	return addr;
> -}
> -static unsigned long func_addr(unsigned long addr)
> -{
> -	return addr;
> -}
> -static unsigned long stub_func_addr(func_desc_t func)
> -{
> -	return func;
> +	return (func_desc_t){addr};

There's only 1 element in the struct, so okay, but it hurt my eyes a
little. I would have been happier with:

	return (func_desc_t){ .addr = addr; };

But of course that also looks bonkers because it starts with "return".
So no matter what I do my eyes bug out. ;)

So it's fine either way. :)

Reviewed-by: Kees Cook <keescook@chromium.org>


>  }
>  
>  /* PowerPC64 specific values for the Elf64_Sym st_other field.  */
> @@ -70,14 +64,6 @@ static func_desc_t func_desc(unsigned long addr)
>  {
>  	return *(struct func_desc *)addr;
>  }
> -static unsigned long func_addr(unsigned long addr)
> -{
> -	return func_desc(addr).addr;
> -}
> -static unsigned long stub_func_addr(func_desc_t func)
> -{
> -	return func.addr;
> -}
>  static unsigned int local_entry_offset(const Elf64_Sym *sym)
>  {
>  	return 0;
> @@ -93,6 +79,16 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
>  }
>  #endif
>  
> +static unsigned long func_addr(unsigned long addr)
> +{
> +	return func_desc(addr).addr;
> +}
> +
> +static unsigned long stub_func_addr(func_desc_t func)
> +{
> +	return func.addr;
> +}
> +
>  #define STUB_MAGIC 0x73747562 /* stub */
>  
>  /* Like PPC32, we need little trampolines to do > 24-bit jumps (into
> -- 
> 2.31.1
>
Segher Boessenkool Feb. 11, 2022, 7:39 a.m. UTC | #4
On Thu, Feb 10, 2022 at 04:54:52PM -0800, Kees Cook wrote:
> On Sun, Oct 17, 2021 at 02:38:17PM +0200, Christophe Leroy wrote:
(edited:)
> > +typedef struct {
> > +	unsigned long addr;
> > +} func_desc_t;
> >  
> >  static func_desc_t func_desc(unsigned long addr)
> >  {
> > +	return (func_desc_t){addr};

> There's only 1 element in the struct, so okay, but it hurt my eyes a
> little. I would have been happier with:
> 
> 	return (func_desc_t){ .addr = addr; };
> 
> But of course that also looks bonkers because it starts with "return".
> So no matter what I do my eyes bug out. ;)

The usual way to avoid convoluted constructs is to name more factors.
So:

static func_desc_t func_desc(unsigned long addr)
{
	func_desc_t desc = {};
	desc.addr = addr;
	return desc;
}


Segher
Christophe Leroy Feb. 14, 2022, 10:30 a.m. UTC | #5
Le 11/02/2022 à 01:54, Kees Cook a écrit :
> On Sun, Oct 17, 2021 at 02:38:17PM +0200, Christophe Leroy wrote:
>> In preparation of making func_desc_t generic, change the ELFv2
>> version to a struct containing 'addr' element.
>>
>> This allows using single helpers common to ELFv1 and ELFv2.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>>   arch/powerpc/kernel/module_64.c | 32 ++++++++++++++------------------
>>   1 file changed, 14 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
>> index a89da0ee25e2..b687ef88c4c4 100644
>> --- a/arch/powerpc/kernel/module_64.c
>> +++ b/arch/powerpc/kernel/module_64.c
>> @@ -33,19 +33,13 @@
>>   #ifdef PPC64_ELF_ABI_v2
>>   
>>   /* An address is simply the address of the function. */
>> -typedef unsigned long func_desc_t;
>> +typedef struct {
>> +	unsigned long addr;
>> +} func_desc_t;
>>   
>>   static func_desc_t func_desc(unsigned long addr)
>>   {
>> -	return addr;
>> -}
>> -static unsigned long func_addr(unsigned long addr)
>> -{
>> -	return addr;
>> -}
>> -static unsigned long stub_func_addr(func_desc_t func)
>> -{
>> -	return func;
>> +	return (func_desc_t){addr};
> 
> There's only 1 element in the struct, so okay, but it hurt my eyes a
> little. I would have been happier with:
> 
> 	return (func_desc_t){ .addr = addr; };
> 
> But of course that also looks bonkers because it starts with "return".
> So no matter what I do my eyes bug out. ;)
> 
> So it's fine either way. :)
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>

I am going for:

  static func_desc_t func_desc(unsigned long addr)
  {
+       func_desc_t desc = {
+               .addr = addr,
+       };
+
+       return desc;
  }


Thanks
Christophe
diff mbox series

Patch

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index a89da0ee25e2..b687ef88c4c4 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -33,19 +33,13 @@ 
 #ifdef PPC64_ELF_ABI_v2
 
 /* An address is simply the address of the function. */
-typedef unsigned long func_desc_t;
+typedef struct {
+	unsigned long addr;
+} func_desc_t;
 
 static func_desc_t func_desc(unsigned long addr)
 {
-	return addr;
-}
-static unsigned long func_addr(unsigned long addr)
-{
-	return addr;
-}
-static unsigned long stub_func_addr(func_desc_t func)
-{
-	return func;
+	return (func_desc_t){addr};
 }
 
 /* PowerPC64 specific values for the Elf64_Sym st_other field.  */
@@ -70,14 +64,6 @@  static func_desc_t func_desc(unsigned long addr)
 {
 	return *(struct func_desc *)addr;
 }
-static unsigned long func_addr(unsigned long addr)
-{
-	return func_desc(addr).addr;
-}
-static unsigned long stub_func_addr(func_desc_t func)
-{
-	return func.addr;
-}
 static unsigned int local_entry_offset(const Elf64_Sym *sym)
 {
 	return 0;
@@ -93,6 +79,16 @@  void *dereference_module_function_descriptor(struct module *mod, void *ptr)
 }
 #endif
 
+static unsigned long func_addr(unsigned long addr)
+{
+	return func_desc(addr).addr;
+}
+
+static unsigned long stub_func_addr(func_desc_t func)
+{
+	return func.addr;
+}
+
 #define STUB_MAGIC 0x73747562 /* stub */
 
 /* Like PPC32, we need little trampolines to do > 24-bit jumps (into