Re: [PATCH 3/3] x86/alternative: make kernel ITS thunks read-only

Re: [PATCH 3/3] x86/alternative: make kernel ITS thunks read-only

[kernel test robot]

Hi Juergen,

kernel test robot noticed the following build errors:

[auto build test ERROR on tip/master]
[also build test ERROR on tip/x86/core linus/master v6.15 next-20250528]
[cannot apply to tip/x86/mm tip/auto-latest]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Juergen-Gross/x86-execmem-don-t-use-PAGE_KERNEL-protection-for-code-pages/20250528-204423
base:   tip/master
patch link:    https://lore.kernel.org/r/20250528123557.12847-4-jgross%40suse.com
patch subject: [PATCH 3/3] x86/alternative: make kernel ITS thunks read-only
config: x86_64-buildonly-randconfig-002-20250529 (https://download.01.org/0day-ci/archive/20250529/202505291124.eAZ7fgbG-lkp@intel.com/config)
compiler: clang version 20.1.2 (https://github.com/llvm/llvm-project 58df0ef89dd64126512e4ee27b4ac3fd8ddf6247)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250529/202505291124.eAZ7fgbG-lkp@intel.com/reproduce)

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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202505291124.eAZ7fgbG-lkp@intel.com/

All errors (new ones prefixed by >>):

>> arch/x86/kernel/alternative.c:2353:6: error: use of undeclared identifier 'its_page'
    2353 |         if (its_page)
         |             ^
>> arch/x86/kernel/alternative.c:2354:3: error: call to undeclared function 'its_set_kernel_ro'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    2354 |                 its_set_kernel_ro(its_page);
         |                 ^
   arch/x86/kernel/alternative.c:2354:21: error: use of undeclared identifier 'its_page'
    2354 |                 its_set_kernel_ro(its_page);
         |                                   ^
   arch/x86/kernel/alternative.c:2355:2: error: use of undeclared identifier 'its_page'
    2355 |         its_page = NULL;
         |         ^
   4 errors generated.


vim +/its_page +2353 arch/x86/kernel/alternative.c

  2308	
  2309	void __init alternative_instructions(void)
  2310	{
  2311		u64 ibt;
  2312	
  2313		int3_selftest();
  2314	
  2315		/*
  2316		 * The patching is not fully atomic, so try to avoid local
  2317		 * interruptions that might execute the to be patched code.
  2318		 * Other CPUs are not running.
  2319		 */
  2320		stop_nmi();
  2321	
  2322		/*
  2323		 * Don't stop machine check exceptions while patching.
  2324		 * MCEs only happen when something got corrupted and in this
  2325		 * case we must do something about the corruption.
  2326		 * Ignoring it is worse than an unlikely patching race.
  2327		 * Also machine checks tend to be broadcast and if one CPU
  2328		 * goes into machine check the others follow quickly, so we don't
  2329		 * expect a machine check to cause undue problems during to code
  2330		 * patching.
  2331		 */
  2332	
  2333		/*
  2334		 * Make sure to set (artificial) features depending on used paravirt
  2335		 * functions which can later influence alternative patching.
  2336		 */
  2337		paravirt_set_cap();
  2338	
  2339		/* Keep CET-IBT disabled until caller/callee are patched */
  2340		ibt = ibt_save(/*disable*/ true);
  2341	
  2342		__apply_fineibt(__retpoline_sites, __retpoline_sites_end,
  2343				__cfi_sites, __cfi_sites_end, true);
  2344	
  2345		/*
  2346		 * Rewrite the retpolines, must be done before alternatives since
  2347		 * those can rewrite the retpoline thunks.
  2348		 */
  2349		apply_retpolines(__retpoline_sites, __retpoline_sites_end);
  2350		apply_returns(__return_sites, __return_sites_end);
  2351	
  2352		/* Make potential last thunk page read-only. */
> 2353		if (its_page)
> 2354			its_set_kernel_ro(its_page);
  2355		its_page = NULL;
  2356	
  2357		/*
  2358		 * Adjust all CALL instructions to point to func()-10, including
  2359		 * those in .altinstr_replacement.
  2360		 */
  2361		callthunks_patch_builtin_calls();
  2362	
  2363		apply_alternatives(__alt_instructions, __alt_instructions_end);
  2364	
  2365		/*
  2366		 * Seal all functions that do not have their address taken.
  2367		 */
  2368		apply_seal_endbr(__ibt_endbr_seal, __ibt_endbr_seal_end);
  2369	
  2370		ibt_restore(ibt);
  2371	

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