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Bug 821463 - SEP CPU flag is disabled on Intel 64 bit when exec_shield is on
Summary: SEP CPU flag is disabled on Intel 64 bit when exec_shield is on
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: kernel
Version: 6.3
Hardware: x86_64
OS: Linux
unspecified
high
Target Milestone: rc
: ---
Assignee: Larry Woodman
QA Contact: Petr Beňas
URL:
Whiteboard:
Depends On:
Blocks: 821741
TreeView+ depends on / blocked
 
Reported: 2012-05-14 15:02 UTC by Orit Wasserman
Modified: 2015-01-04 23:02 UTC (History)
10 users (show)

Fixed In Version: kernel-2.6.32-315.el6
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2013-02-21 06:12:47 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2013:0496 0 normal SHIPPED_LIVE Important: Red Hat Enterprise Linux 6 kernel update 2013-02-20 21:40:54 UTC

Description Orit Wasserman 2012-05-14 15:02:21 UTC 
Description of problem:
SEP cpu flag is disabled on Intel 64 bit when exec_shield is set (which is the default)

Version-Release number of selected component (if applicable):
2.6.32-251.el6.x86_64

How reproducible:
check cpuinfo after install of RHEL6 64 bit.

Steps to Reproduce:
1.check exec_shield is set. cat /proc/sys/kernel/exec-shield returns 1.
2.cat /proc/cpuinfo 
3.
  
Actual results:
sep is not set

Expected results:
sep should be set

Additional info:
this looks like a problem with the exec_shield code in arch/x86/kernel/cpu/common.c :

	if (exec_shield != 0) {
#ifdef CONFIG_X86_PAE
		if (!test_cpu_cap(c, X86_FEATURE_NX))
#endif
			clear_cpu_cap(c, X86_FEATURE_SEP);
	}

CONFIG_X86_PAE is not set for 64 bit so we clear SEP.
Comment 4 Paolo Bonzini 2012-09-04 08:23:13 UTC 
What is really the effect of the bug?  The kernel only uses X86_FEATURE_SEP in 32-bit mode.

In 64-bit mode, sysenter/sysexit are assumed to be present on all Intel CPUs.

arch/x86/kernel/cpu/intel.c:

#ifdef CONFIG_X86_64
        set_cpu_cap(c, X86_FEATURE_SYSENTER32);
#endif

arch/x86/vdso/vdso32-setup.c

#ifdef CONFIG_X86_64
#define vdso32_sysenter()       (boot_cpu_has(X86_FEATURE_SYSENTER32))
#define vdso32_syscall()        (boot_cpu_has(X86_FEATURE_SYSCALL32))
...
#else  /* CONFIG_X86_32 */
#define vdso32_sysenter()       (boot_cpu_has(X86_FEATURE_SEP))
#define vdso32_syscall()        (0)
#endif

I suppose this only affects virtualization of 32-bit guests with -cpu host, where the guest would have to fallback to int $0x80?
Comment 5 Larry Woodman 2012-09-13 15:13:16 UTC 
Sorry but I dont understand what the problem is here.  


In RHEL5 we have:
----------------------------------------------------------------
        if (exec_shield != 0) {
#ifdef CONFIG_HIGHMEM64G   /* NX implies PAE */
                if (!test_bit(X86_FEATURE_NX, c->x86_capability))
#endif
                clear_bit(X86_FEATURE_SEP, c->x86_capability);
        }
----------------------------------------------------------------

In RHEL6 we have:
----------------------------------------------------------------
        if (exec_shield != 0) {
#ifdef CONFIG_X86_PAE
                if (!test_cpu_cap(c, X86_FEATURE_NX))
#endif
                        clear_cpu_cap(c, X86_FEATURE_SEP);
        }
----------------------------------------------------------------

In RHEL5 CONFIG_HIGHMEM64G is set in x86 only and in RHEL6 CONFIG_X86_PAE is set in x86 only.  So the functionality should be the same for x86 & x86_64 in both cases, no?

Larry
Comment 6 Paolo Bonzini 2012-09-13 15:18:32 UTC 
> In RHEL5 CONFIG_HIGHMEM64G is set in x86 only and in RHEL6 CONFIG_X86_PAE is 
> set in x86 only.  So the functionality should be the same for x86 & x86_64 in 
> both cases, no?

The snippet you quoted for RHEL5 is not compiled for x86_64, only i386.  See comment 2.
Comment 7 Larry Woodman 2012-09-13 15:24:46 UTC 
So the whole RHEL6 snipit should be this so we only do this for x86?:

----------------------------------------------------------------
#ifdef CONFIG_X86_PAE
        if (exec_shield != 0) {
                if (!test_cpu_cap(c, X86_FEATURE_NX))
                        clear_cpu_cap(c, X86_FEATURE_SEP);
        }
#endif
----------------------------------------------------------------

Larry
Comment 8 Paolo Bonzini 2012-09-13 15:26:28 UTC 
Yes, that should do it.
Comment 9 RHEL Program Management 2012-09-21 17:11:07 UTC 
This request was evaluated by Red Hat Product Management for
inclusion in a Red Hat Enterprise Linux release.  Product
Management has requested further review of this request by
Red Hat Engineering, for potential inclusion in a Red Hat
Enterprise Linux release for currently deployed products.
This request is not yet committed for inclusion in a release.
Comment 12 Jarod Wilson 2012-10-01 17:14:57 UTC 
Patch(es) available on kernel-2.6.32-315.el6
Comment 16 Petr Beňas 2012-10-04 09:21:10 UTC 
Reproduced in 2.6.32-313.el6.x86_64 and verified in 2.6.32-314.el6.x86_64.
Comment 18 errata-xmlrpc 2013-02-21 06:12:47 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-0496.html
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