x86/fault: Fix wrong signal when vsyscall fails with pkey

The function __bad_area_nosemaphore() calls kernelmode_fixup_or_oops()
with the parameter @signal being actually @pkey, which will send a
signal numbered with the argument in @pkey.

This bug can be triggered when the kernel fails to access user-given
memory pages that are protected by a pkey, so it can go down the
do_user_addr_fault() path and pass the !user_mode() check in
__bad_area_nosemaphore().

Most cases will simply run the kernel fixup code to make an -EFAULT. But
when another condition current->thread.sig_on_uaccess_err is met, which
is only used to emulate vsyscall, the kernel will generate the wrong
signal.

Add a new parameter @pkey to kernelmode_fixup_or_oops() to fix this.

 [ bp: Massage commit message, fix build error as reported by the 0day
   bot: https://lkml.kernel.org/r/202109202245.APvuT8BX-lkp@intel.com ]

Fixes: 5042d40 ("x86/fault: Bypass no_context() for implicit kernel faults from usermode")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jiashuo Liang <liangjs@pku.edu.cn>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20210730030152.249106-1-liangjs@pku.edu.cn

arch/x86/include/asm/pkeys.h

@@ -2,8 +2,6 @@
 #ifndef _ASM_X86_PKEYS_H
 #define _ASM_X86_PKEYS_H
 
-#define ARCH_DEFAULT_PKEY	0
-
 /*
  * If more than 16 keys are ever supported, a thorough audit
  * will be necessary to ensure that the types that store key

arch/x86/mm/fault.c

@@ -710,7 +710,8 @@ page_fault_oops(struct pt_regs *regs, unsigned long error_code,
 
 static noinline void
 kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
-			 unsigned long address, int signal, int si_code)
+			 unsigned long address, int signal, int si_code,
+			 u32 pkey)
 {
 	WARN_ON_ONCE(user_mode(regs));
 
@@ -735,8 +736,12 @@ kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
 
 			set_signal_archinfo(address, error_code);
 
-			/* XXX: hwpoison faults will set the wrong code. */
-			force_sig_fault(signal, si_code, (void __user *)address);
+			if (si_code == SEGV_PKUERR) {
+				force_sig_pkuerr((void __user *)address, pkey);
+			} else {
+				/* XXX: hwpoison faults will set the wrong code. */
+				force_sig_fault(signal, si_code, (void __user *)address);
+			}
 		}
 
 		/*
@@ -798,7 +803,8 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 	struct task_struct *tsk = current;
 
 	if (!user_mode(regs)) {
-		kernelmode_fixup_or_oops(regs, error_code, address, pkey, si_code);
+		kernelmode_fixup_or_oops(regs, error_code, address,
+					 SIGSEGV, si_code, pkey);
 		return;
 	}
 
@@ -930,7 +936,8 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 {
 	/* Kernel mode? Handle exceptions or die: */
 	if (!user_mode(regs)) {
-		kernelmode_fixup_or_oops(regs, error_code, address, SIGBUS, BUS_ADRERR);
+		kernelmode_fixup_or_oops(regs, error_code, address,
+					 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
 		return;
 	}
 
@@ -1396,7 +1403,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 		 */
 		if (!user_mode(regs))
 			kernelmode_fixup_or_oops(regs, error_code, address,
-						 SIGBUS, BUS_ADRERR);
+						 SIGBUS, BUS_ADRERR,
+						 ARCH_DEFAULT_PKEY);
 		return;
 	}
 
@@ -1416,15 +1424,17 @@ void do_user_addr_fault(struct pt_regs *regs,
 		return;
 
 	if (fatal_signal_pending(current) && !user_mode(regs)) {
-		kernelmode_fixup_or_oops(regs, error_code, address, 0, 0);
+		kernelmode_fixup_or_oops(regs, error_code, address,
+					 0, 0, ARCH_DEFAULT_PKEY);
 		return;
 	}
 
 	if (fault & VM_FAULT_OOM) {
 		/* Kernel mode? Handle exceptions or die: */
 		if (!user_mode(regs)) {
 			kernelmode_fixup_or_oops(regs, error_code, address,
-						 SIGSEGV, SEGV_MAPERR);
+						 SIGSEGV, SEGV_MAPERR,
+						 ARCH_DEFAULT_PKEY);
 			return;
 		}
 

include/linux/pkeys.h

@@ -4,6 +4,8 @@
 
 #include <linux/mm.h>
 
+#define ARCH_DEFAULT_PKEY	0
+
 #ifdef CONFIG_ARCH_HAS_PKEYS
 #include <asm/pkeys.h>
 #else /* ! CONFIG_ARCH_HAS_PKEYS */