Re: [PATCH v5 5/7] arm64: uprobes: Add GCS support to uretprobes

[kernel test robot <lkp@intel.com>]

Hi Jeremy,

kernel test robot noticed the following build errors:

[auto build test ERROR on arm64/for-next/core]
[also build test ERROR on perf-tools-next/perf-tools-next tip/perf/core perf-tools/perf-tools linus/master v6.17-rc1 next-20250812]
[cannot apply to acme/perf/core]
[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/Jeremy-Linton/arm64-probes-Break-ret-out-from-bl-blr/20250811-221529
base:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
patch link:    https://lore.kernel.org/r/20250811141010.741989-6-jeremy.linton%40arm.com
patch subject: [PATCH v5 5/7] arm64: uprobes: Add GCS support to uretprobes
config: arm64-randconfig-r111-20250813 (https://download.01.org/0day-ci/archive/20250813/202508131334.FfoZQ27h-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 13.4.0
reproduce: (https://download.01.org/0day-ci/archive/20250813/202508131334.FfoZQ27h-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/202508131334.FfoZQ27h-lkp@intel.com/

All errors (new ones prefixed by >>):

   arch/arm64/kernel/probes/uprobes.c: In function 'arch_uretprobe_hijack_return_addr':
>> arch/arm64/kernel/probes/uprobes.c:171:33: error: implicit declaration of function 'get_user_gcs'; did you mean 'put_user_gcs'? [-Werror=implicit-function-declaration]
     171 |                 gcs_ret_vaddr = get_user_gcs((unsigned long __user *)gcspr, &err);
         |                                 ^~~~~~~~~~~~
         |                                 put_user_gcs
   cc1: some warnings being treated as errors


vim +171 arch/arm64/kernel/probes/uprobes.c

   157	
   158	unsigned long
   159	arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,
   160					  struct pt_regs *regs)
   161	{
   162		unsigned long orig_ret_vaddr;
   163		unsigned long gcs_ret_vaddr;
   164		int err = 0;
   165		u64 gcspr;
   166	
   167		orig_ret_vaddr = procedure_link_pointer(regs);
   168	
   169		if (task_gcs_el0_enabled(current)) {
   170			gcspr = read_sysreg_s(SYS_GCSPR_EL0);
 > 171			gcs_ret_vaddr = get_user_gcs((unsigned long __user *)gcspr, &err);
   172			if (err) {
   173				force_sig(SIGSEGV);
   174				goto out;
   175			}
   176	
   177			/*
   178			 * If the LR and GCS return addr don't match, then some kind of PAC
   179			 * signing or control flow occurred since entering the probed function.
   180			 * Likely because the user is attempting to retprobe on an instruction
   181			 * that isn't a function boundary or inside a leaf function. Explicitly
   182			 * abort this retprobe because it will generate a GCS exception.
   183			 */
   184			if (gcs_ret_vaddr != orig_ret_vaddr) {
   185				orig_ret_vaddr = -1;
   186				goto out;
   187			}
   188	
   189			put_user_gcs(trampoline_vaddr, (unsigned long __user *)gcspr, &err);
   190			if (err) {
   191				force_sig(SIGSEGV);
   192				goto out;
   193			}
   194		}
   195	
   196		/* Replace the return addr with trampoline addr */
   197		procedure_link_pointer_set(regs, trampoline_vaddr);
   198	
   199	out:
   200		return orig_ret_vaddr;
   201	}
   202	

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