x86/entry: Rename ignore_sysret()

jira VULN-772
cve-pre CVE-2024-25744
commit-author Nikolay Borisov <nik.borisov@suse.com>
commit f71e1d2

The SYSCALL instruction cannot really be disabled in compatibility mode.
The best that can be done is to configure the CSTAR msr to point to a
minimal handler. Currently this handler has a rather misleading name -
ignore_sysret() as it's not really doing anything with sysret.

Give it a more descriptive name.

	Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
	Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230623111409.3047467-3-nik.borisov@suse.com

(cherry picked from commit f71e1d2)
	Signed-off-by: Marcin Wcisło <marcin.wcislo@conclusive.pl>

Author: pvts-mat

arch/x86/entry/entry_64.S

@@ -1503,12 +1503,12 @@ SYM_CODE_END(asm_exc_nmi)
  * This handles SYSCALL from 32-bit code.  There is no way to program
  * MSRs to fully disable 32-bit SYSCALL.
  */
-SYM_CODE_START(ignore_sysret)
+SYM_CODE_START(entry_SYSCALL32_ignore)
 	UNWIND_HINT_EMPTY
 	ENDBR
 	mov	$-ENOSYS, %eax
 	sysretl
-SYM_CODE_END(ignore_sysret)
+SYM_CODE_END(entry_SYSCALL32_ignore)
 #endif
 
 .pushsection .text, "ax"

arch/x86/include/asm/processor.h

@@ -461,7 +461,7 @@ static inline unsigned long cpu_kernelmode_gs_base(int cpu)
 
 DECLARE_PER_CPU(void *, hardirq_stack_ptr);
 DECLARE_PER_CPU(bool, hardirq_stack_inuse);
-extern asmlinkage void ignore_sysret(void);
+extern asmlinkage void entry_SYSCALL32_ignore(void);
 
 /* Save actual FS/GS selectors and bases to current->thread */
 void current_save_fsgs(void);

arch/x86/kernel/cpu/common.c

@@ -2025,7 +2025,7 @@ void syscall_init(void)
 		    (unsigned long)(cpu_entry_stack(smp_processor_id()) + 1));
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
 #else
-	wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
+	wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL32_ignore);
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
 	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);