* [PATCH 06/10] x86/entry/32: Clear the CS high bits
[not found] <20181020235230.37324-1-shayan.doust@outlook.com>
@ 2018-10-20 23:52 ` Shayan Doust
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From: Shayan Doust @ 2018-10-20 23:52 UTC (permalink / raw)
To: hello
Cc: Jan Kiszka, Borislav Petkov, H. Peter Anvin, Andrea Arcangeli,
Andy Lutomirski, Boris Ostrovsky, Brian Gerst, Dave Hansen,
David Laight, Denys Vlasenko, Eduardo Valentin, Greg KH,
Ingo Molnar, Jiri Kosina, Josh Poimboeuf, Juergen Gross,
Linus Torvalds, Peter Zijlstra, Thomas Gleixner, Will Deacon,
aliguori, daniel.gruss, hughd, keescook, linux-mm, x86-ml
From: Jan Kiszka <jan.kiszka@siemens.com>
Even if not on an entry stack, the CS's high bits must be
initialized because they are unconditionally evaluated in
PARANOID_EXIT_TO_KERNEL_MODE.
Failing to do so broke the boot on Galileo Gen2 and IOT2000 boards.
[ bp: Make the commit message tone passive and impartial. ]
Fixes: b92a165df17e ("x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack")
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andrea Arcangeli <aarcange@redhat.com>
CC: Andy Lutomirski <luto@kernel.org>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Brian Gerst <brgerst@gmail.com>
CC: Dave Hansen <dave.hansen@intel.com>
CC: David Laight <David.Laight@aculab.com>
CC: Denys Vlasenko <dvlasenk@redhat.com>
CC: Eduardo Valentin <eduval@amazon.com>
CC: Greg KH <gregkh@linuxfoundation.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Jiri Kosina <jkosina@suse.cz>
CC: Josh Poimboeuf <jpoimboe@redhat.com>
CC: Juergen Gross <jgross@suse.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Will Deacon <will.deacon@arm.com>
CC: aliguori@amazon.com
CC: daniel.gruss@iaik.tugraz.at
CC: hughd@google.com
CC: keescook@google.com
CC: linux-mm <linux-mm@kvack.org>
CC: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/f271c747-1714-5a5b-a71f-ae189a093b8d@siemens.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/entry_32.S | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 2767c625a52c..fbbf1ba57ec6 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -389,6 +389,13 @@
* that register for the time this macro runs
*/
+ /*
+ * The high bits of the CS dword (__csh) are used for
+ * CS_FROM_ENTRY_STACK and CS_FROM_USER_CR3. Clear them in case
+ * hardware didn't do this for us.
+ */
+ andl $(0x0000ffff), PT_CS(%esp)
+
/* Are we on the entry stack? Bail out if not! */
movl PER_CPU_VAR(cpu_entry_area), %ecx
addl $CPU_ENTRY_AREA_entry_stack + SIZEOF_entry_stack, %ecx
@@ -407,12 +414,6 @@
/* Load top of task-stack into %edi */
movl TSS_entry2task_stack(%edi), %edi
- /*
- * Clear unused upper bits of the dword containing the word-sized CS
- * slot in pt_regs in case hardware didn't clear it for us.
- */
- andl $(0x0000ffff), PT_CS(%esp)
-
/* Special case - entry from kernel mode via entry stack */
#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %ecx # mix EFLAGS and CS
--
2.17.1
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