x86/entry/64: Allocate and enable the SYSENTER stack

CVE-2017-5754

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>
(cherry picked from commit 1a79797b58cddfa948420a7553241c79c013e3ca)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index be745b7a3e3e8dd62e282e9cf945c9fd3b4755ae..1f76b66518eea13832318c8b6387c9caa2bd710b 100644 (file)
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -47,7 +47,7 @@
  */
 ENTRY(entry_SYSENTER_compat)
        /* Interrupts are off on entry. */
-       SWAPGS_UNSAFE_STACK
+       SWAPGS
        movq    PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
        /*

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 79739e5f939a29d0aa653ca062945584817acb49..5225917f9760c3699390ce6f25321b529264f684 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -333,14 +333,11 @@ 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);

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index de827d6ac8c2e8ad751eba8699cd1e0ada0e7f4b..031bd35bd9119e7d86a4f4a36f20d787d8c2fdb0 100644 (file)
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -92,4 +92,9 @@ 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));
 }

diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index 880aa093268df7a0d7db23abde984647880c47cc..d09b161a3bd0a31a5867965cbf4f9e314626b799 100644 (file)
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -52,11 +52,6 @@ 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);

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 121fe3570d6fca1d5f8744d6852ce4d3aaea35a6..aa97e4cd3a3355c5b5a4b8cfc73bd257b9297654 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1362,7 +1362,9 @@ 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);

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ccf3a4f4ef686a326ae7e080661823418b3bb7c3..aa86e810fb5461780faae5161a06ca3cc747055e 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -70,9 +70,7 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
          */
        .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);
 

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3a46cab2696e5ca9146ce48810ad1c587e5f9410..7b1d0df624cf4aef7c5f1929c84a68d712310082 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -806,14 +806,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
        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);