x86/asm: Make sure verify_cpu() has a good stack

04633df0c43d ("x86/cpu: Call verify_cpu() after having entered long mode too")
added the call to verify_cpu() for sanitizing CPU configuration.

The latter uses the stack minimally and it can happen that we land in
startup_64() directly from a 64-bit bootloader. Then we want to use our
own, known good stack.

Do that.

APs don't need this as the trampoline sets up a stack for them.

Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mika Penttilä <mika.penttila@nextfour.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1459434062-31055-1-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 3de91a7..5df831e 100644 (file)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -65,6 +65,14 @@ startup_64:
         * tables and then reload them.
         */
 
+       /*
+        * Setup stack for verify_cpu(). "-8" because stack_start is defined
+        * this way, see below. Our best guess is a NULL ptr for stack
+        * termination heuristics and we don't want to break anything which
+        * might depend on it (kgdb, ...).
+        */
+       leaq    (__end_init_task - 8)(%rip), %rsp
+
        /* Sanitize CPU configuration */
        call verify_cpu
 

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 339125b..6a67ab9 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -245,7 +245,9 @@
 
 #define INIT_TASK_DATA(align)                                          \
        . = ALIGN(align);                                               \
-       *(.data..init_task)
+       VMLINUX_SYMBOL(__start_init_task) = .;                          \
+       *(.data..init_task)                                             \
+       VMLINUX_SYMBOL(__end_init_task) = .;
 
 /*
  * Read only Data