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    Subject[tip:x86/urgent] x86/entry/32: Clear the CS high bits
    Commit-ID:  04f4f954b69526d7af8ffb8e5780f08b8a6cda2d
    Gitweb: https://git.kernel.org/tip/04f4f954b69526d7af8ffb8e5780f08b8a6cda2d
    Author: Jan Kiszka <jan.kiszka@siemens.com>
    AuthorDate: Mon, 15 Oct 2018 16:09:29 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 17 Oct 2018 12:30:20 +0200

    x86/entry/32: Clear the CS high bits

    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
    \
     
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