Re: [PATCH 5.15 00/59] 5.15.184-rc1 review

[Richard Narron <richard@aaazen.com>]

On Tue, 27 May 2025, Pawan Gupta wrote:

> On Tue, May 27, 2025 at 12:31:47PM -0700, Richard Narron wrote:
> > On Fri, 23 May 2025, Guenter Roeck wrote:
> >
> > > On 5/20/25 06:49, Greg Kroah-Hartman wrote:
> > > > This is the start of the stable review cycle for the 5.15.184 release.
> > > > There are 59 patches in this series, all will be posted as a response
> > > > to this one.  If anyone has any issues with these being applied, please
> > > > let me know.
> > > >
> > > > Responses should be made by Thu, 22 May 2025 12:57:37 +0000.
> > > > Anything received after that time might be too late.
> > > >
> > >
> > > Build reference: v5.15.184
> > > Compiler version: x86_64-linux-gcc (GCC) 12.4.0
> > > Assembler version: GNU assembler (GNU Binutils) 2.40
> > >
> > > Configuration file workarounds:
> > >     "s/CONFIG_FRAME_WARN=.*/CONFIG_FRAME_WARN=0/"
> > >
> > > Building i386:defconfig ... passed
> > > Building i386:allyesconfig ... failed
> > > --------------
> > > Error log:
> > > x86_64-linux-ld: arch/x86/kernel/static_call.o: in function
> > > `__static_call_transform':
> > > static_call.c:(.ref.text+0x46): undefined reference to `cpu_wants_rethunk_at'
> > > make[1]: [Makefile:1234: vmlinux] Error 1 (ignored)
> > > --------------
> > > Building i386:allmodconfig ... failed
> > > --------------
> > > Error log:
> > > x86_64-linux-ld: arch/x86/kernel/static_call.o: in function
> > > `__static_call_transform':
> > > static_call.c:(.ref.text+0x46): undefined reference to `cpu_wants_rethunk_at'
> > > make[1]: [Makefile:1234: vmlinux] Error 1 (ignored)
> > > --------------
> > >
> > > In v5.15.y, cpu_wants_rethunk_at is only built if CONFIG_STACK_VALIDATION=y,
> > > but that is not supported for i386 builds. The dummy function in
> > > arch/x86/include/asm/alternative.h doesn't take that dependency into account.
> > >
> >
> > I found this bug too using the Slackware 15.0 32-bit kernel
> > configuration.
> >
> > Here is a simple work around patch, but there may be a better solution...
> >
> > --- arch/x86/kernel/static_call.c.orig	2025-05-22 05:08:28.000000000 -0700
> > +++ arch/x86/kernel/static_call.c	2025-05-27 10:25:27.630496538 -0700
> > @@ -81,9 +81,12 @@
> >  		break;
> >
> >  	case RET:
> > +
> > +#ifdef CONFIG_64BIT
> >  		if (cpu_wants_rethunk_at(insn))
> >  			code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk);
> >  		else
> > +#endif
> >  			code = &retinsn;
> >  		break;
> >
>
> Another option is to define the empty function when CONFIG_STACK_VALIDATION=n as below:
>
> --- 8< ---
> From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Subject: [PATCH] x86/its: Fix undefined reference to cpu_wants_rethunk_at()
>
> Below error was reported in 32-bit kernel build:
>
>   static_call.c:(.ref.text+0x46): undefined reference to `cpu_wants_rethunk_at'
>   make[1]: [Makefile:1234: vmlinux] Error
>
> This is because the definition of cpu_wants_rethunk_at() depends on
> CONFIG_STACK_VALIDATION which is only enabled in 64-bit mode.
>
> Define the empty function when CONFIG_STACK_VALIDATION=n, rethunk mitigation
> is anyways not supported without it.
>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Link: https://lore.kernel.org/stable/0f597436-5da6-4319-b918-9f57bde5634a@roeck-us.net/
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> ---
>  arch/x86/include/asm/alternative.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 1797f80c10de..a5f704dbb4a1 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -98,7 +98,7 @@ static inline u8 *its_static_thunk(int reg)
>  }
>  #endif
>
> -#ifdef CONFIG_RETHUNK
> +#if defined(CONFIG_RETHUNK) && defined(CONFIG_STACK_VALIDATION)
>  extern bool cpu_wants_rethunk(void);
>  extern bool cpu_wants_rethunk_at(void *addr);
>  #else
> --
> 2.34.1
>

Thanks for looking at this Pawan.

Your new patch works fine on both Slackware 15.0 32-bit and 64-bit
systems.