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

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

On Wed, May 28, 2025 at 09:49:40PM -0700, Richard Narron wrote:
> 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.

Thank you for verifying the patch.