linux-kernel - Re: [tip:x86/boot 10/10] arch/x86/boot/compressed/sev-handle-vc.c:104 do_boot_stage2_vc() error: we previously assumed 'boot

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Message-ID: <aB8mXZ_TxDuLa7Jr@stanley.mountain>
Date: Sat, 10 May 2025 13:11:41 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: oe-kbuild@...ts.linux.dev, lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [tip:x86/boot 10/10]
 arch/x86/boot/compressed/sev-handle-vc.c:104 do_boot_stage2_vc() error: we
 previously assumed 'boot_ghcb' could be null (see line 101)

On Sat, May 10, 2025 at 09:57:23AM +0200, Ard Biesheuvel wrote:
> Hi Dan,
> 
> On Sat, 10 May 2025 at 09:43, Dan Carpenter <dan.carpenter@...aro.org> wrote:
> >
> > Hi Ard,
> >
> > FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/boot
> > head:   ed4d95d033e359f9445e85bf5a768a5859a5830b
> > commit: ed4d95d033e359f9445e85bf5a768a5859a5830b [10/10] x86/sev: Disentangle #VC handling code from startup code
> > config: x86_64-randconfig-161-20250510 (https://download.01.org/0day-ci/archive/20250510/202505100719.9pE7wDfB-lkp@intel.com/config)
> > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > | Closes: https://lore.kernel.org/r/202505100719.9pE7wDfB-lkp@intel.com/
> >
> > smatch warnings:
> > arch/x86/boot/compressed/sev-handle-vc.c:104 do_boot_stage2_vc() error: we previously assumed 'boot_ghcb' could be null (see line 101)
> >
> > vim +/boot_ghcb +104 arch/x86/boot/compressed/sev-handle-vc.c
> >
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04   96  void do_boot_stage2_vc(struct pt_regs *regs, unsigned long exit_code)
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04   97  {
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04   98   struct es_em_ctxt ctxt;
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04   99   enum es_result result;
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04  100
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04 @101   if (!boot_ghcb && !early_setup_ghcb())
> >                                                     ^^^^^^^^^^
> > Check for NULL.  Should the && be ||?
> >
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04  102           sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04  103
> > ed4d95d033e359 Ard Biesheuvel 2025-05-04 @104   vc_ghcb_invalidate(boot_ghcb);
> >                                                                    ^^^^^^^^^
> > Unchecked dereference.
> >
> 
> On success, early_setup_ghcb() will assign boot_ghcb, and so it is
> only called if it was unset.
> 
> The logic is a bit clunky here: for clarity, it could be rewritten as
> 
> if (!boot_ghcb) {
>   early_setup_ghcb();
>   if (!boot_ghcb)
>     sev_es_terminate(...);
> }

Ah.  Thanks.  I didn't even think that early_setup_ghcb() might
set boot_ghcb().

regards,
dan carpenter