linux-kernel - [PATCH v2] x86/fault: Fix wrong signal when vsyscall fails with pkey

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Date:   Fri, 30 Jul 2021 11:01:52 +0800
From:   Jiashuo Liang <liangjs@....edu.cn>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org, Jiashuo Liang <liangjs@....edu.cn>
Subject: [PATCH v2] x86/fault: Fix wrong signal when vsyscall fails with pkey

The function __bad_area_nosemaphore() calls kernelmode_fixup_or_oops() with
parameter "signal" being "pkey", which will send a signal numbered "pkey".

This bug appears when the kernel fail to access user-given memory pages
that are protected by pkey, so it can go through 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, we will generate the wrong signal.

A new parameter "pkey" is added to kernelmode_fixup_or_oops() to fix it.

Fixes: 5042d40a264c ("x86/fault: Bypass no_context() for implicit kernel faults from usermode")
Signed-off-by: Jiashuo Liang <liangjs@....edu.cn>
---

Changes in v2:
  - Use ARCH_DEFAULT_PKEY instead of 0 for unused pkey parameter.

 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 b2eefdefc108..84a2c8c4af73 100644
--- a/arch/x86/mm/fault.c
+++ b/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;
 	}
 
@@ -1416,7 +1424,8 @@ 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;
 	}
 
@@ -1424,7 +1433,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 		/* 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;
 		}
 
-- 
2.32.0