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    Subject[PATCH 4.14 079/159] x86/entry/64: Allocate and enable the SYSENTER stack
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Andy Lutomirski <luto@kernel.org>

    commit 1a79797b58cddfa948420a7553241c79c013e3ca upstream.

    This will simplify future changes that want scratch variables early in
    the SYSENTER handler -- they'll be able to spill registers to the
    stack. It also lets us get rid of a SWAPGS_UNSAFE_STACK user.

    This does not depend on CONFIG_IA32_EMULATION=y because we'll want the
    stack space even without IA32 emulation.

    As far as I can tell, the reason that this wasn't done from day 1 is
    that we use IST for #DB and #BP, which is IMO rather nasty and causes
    a lot more problems than it solves. But, since #DB uses IST, we don't
    actually need a real stack for SYSENTER (because SYSENTER with TF set
    will invoke #DB on the IST stack rather than the SYSENTER stack).

    I want to remove IST usage from these vectors some day, and this patch
    is a prerequisite for that as well.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Borislav Petkov <bp@suse.de>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Borislav Petkov <bpetkov@suse.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Dave Hansen <dave.hansen@linux.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: H. Peter Anvin <hpa@zytor.com>
    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: Rik van Riel <riel@redhat.com>
    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
    Link: https://lkml.kernel.org/r/20171204150605.312726423@linutronix.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/entry/entry_64_compat.S | 2 +-
    arch/x86/include/asm/processor.h | 3 ---
    arch/x86/kernel/asm-offsets.c | 5 +++++
    arch/x86/kernel/asm-offsets_32.c | 5 -----
    arch/x86/kernel/cpu/common.c | 4 +++-
    arch/x86/kernel/process.c | 2 --
    arch/x86/kernel/traps.c | 3 +--
    7 files changed, 10 insertions(+), 14 deletions(-)

    --- a/arch/x86/entry/entry_64_compat.S
    +++ b/arch/x86/entry/entry_64_compat.S
    @@ -48,7 +48,7 @@
    */
    ENTRY(entry_SYSENTER_compat)
    /* Interrupts are off on entry. */
    - SWAPGS_UNSAFE_STACK
    + SWAPGS
    movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

    /*
    --- a/arch/x86/include/asm/processor.h
    +++ b/arch/x86/include/asm/processor.h
    @@ -339,14 +339,11 @@ struct tss_struct {
    */
    unsigned long io_bitmap[IO_BITMAP_LONGS + 1];

    -#ifdef CONFIG_X86_32
    /*
    * Space for the temporary SYSENTER stack.
    */
    unsigned long SYSENTER_stack_canary;
    unsigned long SYSENTER_stack[64];
    -#endif
    -
    } ____cacheline_aligned;

    DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss);
    --- a/arch/x86/kernel/asm-offsets.c
    +++ b/arch/x86/kernel/asm-offsets.c
    @@ -93,4 +93,9 @@ void common(void) {

    BLANK();
    DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
    +
    + /* Offset from cpu_tss to SYSENTER_stack */
    + OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
    + /* Size of SYSENTER_stack */
    + DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
    }
    --- a/arch/x86/kernel/asm-offsets_32.c
    +++ b/arch/x86/kernel/asm-offsets_32.c
    @@ -50,11 +50,6 @@ void foo(void)
    DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
    offsetofend(struct tss_struct, SYSENTER_stack));

    - /* Offset from cpu_tss to SYSENTER_stack */
    - OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
    - /* Size of SYSENTER_stack */
    - DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
    -
    #ifdef CONFIG_CC_STACKPROTECTOR
    BLANK();
    OFFSET(stack_canary_offset, stack_canary, canary);
    --- a/arch/x86/kernel/cpu/common.c
    +++ b/arch/x86/kernel/cpu/common.c
    @@ -1361,7 +1361,9 @@ void syscall_init(void)
    * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
    */
    wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
    - wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
    + wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
    + (unsigned long)this_cpu_ptr(&cpu_tss) +
    + offsetofend(struct tss_struct, SYSENTER_stack));
    wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
    #else
    wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
    --- a/arch/x86/kernel/process.c
    +++ b/arch/x86/kernel/process.c
    @@ -71,9 +71,7 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(
    */
    .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
    #endif
    -#ifdef CONFIG_X86_32
    .SYSENTER_stack_canary = STACK_END_MAGIC,
    -#endif
    };
    EXPORT_PER_CPU_SYMBOL(cpu_tss);

    --- a/arch/x86/kernel/traps.c
    +++ b/arch/x86/kernel/traps.c
    @@ -794,14 +794,13 @@ dotraplinkage void do_debug(struct pt_re
    debug_stack_usage_dec();

    exit:
    -#if defined(CONFIG_X86_32)
    /*
    * This is the most likely code path that involves non-trivial use
    * of the SYSENTER stack. Check that we haven't overrun it.
    */
    WARN(this_cpu_read(cpu_tss.SYSENTER_stack_canary) != STACK_END_MAGIC,
    "Overran or corrupted SYSENTER stack\n");
    -#endif
    +
    ist_exit(regs);
    }
    NOKPROBE_SYMBOL(do_debug);

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