linux-kernel - [tip:x86/vdso] x86_64: Add a comment explaining the TASK_SIZE

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] [day] [month] [year] [list]

Date:	Mon, 10 Nov 2014 01:45:33 -0800
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, luto@...capital.net
Subject: [tip:x86/vdso] x86_64:
  Add a comment explaining the TASK_SIZE_MAX guard page

Commit-ID:  07114f0f1cda8b2ef6e884d0c7b268a32cce7903
Gitweb:     http://git.kernel.org/tip/07114f0f1cda8b2ef6e884d0c7b268a32cce7903
Author:     Andy Lutomirski <luto@...capital.net>
AuthorDate: Tue, 4 Nov 2014 15:46:21 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 10 Nov 2014 10:43:13 +0100

x86_64: Add a comment explaining the TASK_SIZE_MAX guard page

That guard page is absolutely necessary; explain why for
posterity.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
Link: http://lkml.kernel.org/r/23320cb5017c2da8475ec20fcde8089d82aa2699.1415144745.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/processor.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index eb71ec7..82d93ea 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -893,7 +893,13 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
 
 #else
 /*
- * User space process size. 47bits minus one guard page.
+ * User space process size. 47bits minus one guard page.  The guard
+ * page is necessary on Intel CPUs: if a SYSCALL instruction is at
+ * the highest possible canonical userspace address, then that
+ * syscall will enter the kernel with a non-canonical return
+ * address, and SYSRET will explode dangerously.  We avoid this
+ * particular problem by preventing anything from being mapped
+ * at the maximum canonical address.
  */
 #define TASK_SIZE_MAX	((1UL << 47) - PAGE_SIZE)
 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/