linux-kernel - [tip: x86/urgent] x86/fault: Fix wrong signal when vsyscall fails with pkey

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Date:   Mon, 20 Sep 2021 10:42:39 -0000
From:   "tip-bot2 for Jiashuo Liang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jiashuo Liang <liangjs@....edu.cn>, Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/fault: Fix wrong signal when vsyscall fails with pkey

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     0829d0b6bf0fb3453608798442deaf00c4a1abec
Gitweb:        https://git.kernel.org/tip/0829d0b6bf0fb3453608798442deaf00c4a1abec
Author:        Jiashuo Liang <liangjs@....edu.cn>
AuthorDate:    Fri, 30 Jul 2021 11:01:52 +08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Mon, 20 Sep 2021 12:31:06 +02:00

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. ]

Fixes: 5042d40a264c ("x86/fault: Bypass no_context() for implicit kernel faults from usermode")
Signed-off-by: Jiashuo Liang <liangjs@....edu.cn>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lkml.kernel.org/r/20210730030152.249106-1-liangjs@pku.edu.cn
---
 arch/x86/mm/fault.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index b2eefde..84a2c8c 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -710,7 +710,8 @@ oops:
 
 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 @@ good_area:
 		 */
 		if (!user_mode(regs))
 			kernelmode_fixup_or_oops(regs, error_code, address,
-						 SIGBUS, BUS_ADRERR);
+						 SIGBUS, BUS_ADRERR,
+						 ARCH_DEFAULT_PKEY);
 		return;
 	}
 
@@ -1416,7 +1424,8 @@ good_area:
 		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;
 	}
 
@@ -1424,7 +1433,8 @@ good_area:
 		/* 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;
 		}