linux-kernel - [PATCH 5/5] x86/entry: don't copy to tmp in fixup_bad

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200527073107.2127-6-laijs@linux.alibaba.com>
Date:   Wed, 27 May 2020 07:31:07 +0000
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH 5/5] x86/entry: don't copy to tmp in fixup_bad_iret

It is safe to do memcpy() in fixup_bad_iret() now.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kernel/traps.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 8291f84933ff..6fe72c771745 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -657,17 +657,23 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 	 * (rather than just below the IRET frame) and we want to
 	 * pretend that the exception came from the IRET target.
 	 */
-	struct bad_iret_stack tmp, *new_stack =
+	struct bad_iret_stack *new_stack =
 		(struct bad_iret_stack *)__this_cpu_read(cpu_current_top_of_stack) - 1;
 
-	/* Copy the IRET target to the temporary storage. */
-	memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
+	/*
+	 * Both the IRET frame and the saved pt_regs must be on the
+	 * entry stacks since iret to user is only issued on the
+	 * entry stacks. So they don't overlap with kernel stack and
+	 * memcpy() is safe to copy them.
+	 */
+	BUG_ON(((unsigned long)s - (unsigned long)new_stack) < PAGE_SIZE ||
+	       ((unsigned long)new_stack - (unsigned long)s) < PAGE_SIZE);
 
-	/* Copy the remainder of the stack from the current stack. */
-	memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+	/* Copy the IRET target to the new stack. */
+	memcpy(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
 
-	/* Update the entry stack */
-	memcpy(new_stack, &tmp, sizeof(tmp));
+	/* Copy the remainder of the stack from the current stack. */
+	memcpy(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
 
 	BUG_ON(!user_mode(&new_stack->regs));
 	return new_stack;
-- 
2.20.1