x86/entry: Move SYSENTER_stack to the beginning of struct tss_struct

SYSENTER_stack should have reliable overflow detection, which
means that it needs to be at the bottom of a page, not the top.
Move it to the beginning of struct tss_struct and page-align it.

Also add an assertion to make sure that the fixed hardware TSS
doesn't cross a page boundary.

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/20171204150605.881827433@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 555c947..7590512 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -332,7 +332,16 @@ struct x86_hw_tss {
 
 struct tss_struct {
        /*
-        * The hardware state:
+        * Space for the temporary SYSENTER stack, used for SYSENTER
+        * and the entry trampoline as well.
+        */
+       unsigned long           SYSENTER_stack_canary;
+       unsigned long           SYSENTER_stack[64];
+
+       /*
+        * The fixed hardware portion.  This must not cross a page boundary
+        * at risk of violating the SDM's advice and potentially triggering
+        * errata.
         */
        struct x86_hw_tss       x86_tss;
 
@@ -343,15 +352,9 @@ struct tss_struct {
         * be within the limit.
         */
        unsigned long           io_bitmap[IO_BITMAP_LONGS + 1];
+} __aligned(PAGE_SIZE);
 
-       /*
-        * Space for the temporary SYSENTER stack.
-        */
-       unsigned long           SYSENTER_stack_canary;
-       unsigned long           SYSENTER_stack[64];
-} ____cacheline_aligned;
-
-DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss);
+DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss);
 
 /*
  * sizeof(unsigned long) coming from an extra "long" at the end

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3f285b9..60b2dfd 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -487,6 +487,27 @@ static inline void setup_cpu_entry_area(int cpu)
 #endif
 
        __set_fixmap(get_cpu_entry_area_index(cpu, gdt), get_cpu_gdt_paddr(cpu), gdt_prot);
+
+       /*
+        * The Intel SDM says (Volume 3, 7.2.1):
+        *
+        *  Avoid placing a page boundary in the part of the TSS that the
+        *  processor reads during a task switch (the first 104 bytes). The
+        *  processor may not correctly perform address translations if a
+        *  boundary occurs in this area. During a task switch, the processor
+        *  reads and writes into the first 104 bytes of each TSS (using
+        *  contiguous physical addresses beginning with the physical address
+        *  of the first byte of the TSS). So, after TSS access begins, if
+        *  part of the 104 bytes is not physically contiguous, the processor
+        *  will access incorrect information without generating a page-fault
+        *  exception.
+        *
+        * There are also a lot of errata involving the TSS spanning a page
+        * boundary.  Assert that we're not doing that.
+        */
+       BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
+                     offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
+
 }
 
 /* Load the original GDT from the per-cpu structure */