From 22dc391865af29a1332bd1d17152f2ca7188bc4a Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 21 Sep 2016 16:04:06 -0500 Subject: [PATCH] x86/boot: Fix the end of the stack for idle tasks Thanks to all the recent x86 entry code refactoring, most tasks' kernel stacks start at the same offset right below their saved pt_regs, regardless of which syscall was used to enter the kernel. That creates a nice convention which makes it straightforward to identify the end of the stack, which can be useful for the unwinder to verify the stack is sane. However, the boot CPU's idle "swapper" task doesn't follow that convention. Fix that by starting its stack at a sizeof(pt_regs) offset from the end of the stack page. Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Nilay Vaish Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/81aee3beb6ed88e44f1bea6986bb7b65c368f77a.1474480779.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/head_32.S | 9 ++++++++- arch/x86/kernel/head_64.S | 15 +++++++-------- 2 files changed, 15 insertions(+), 9 deletions(-) diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index 9a6f8e820ae1..df541ac2071e 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -63,6 +63,8 @@ #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD) #endif +#define SIZEOF_PTREGS 17*4 + /* * Number of possible pages in the lowmem region. * @@ -708,7 +710,12 @@ ENTRY(initial_page_table) .data .balign 4 ENTRY(initial_stack) - .long init_thread_union+THREAD_SIZE + /* + * The SIZEOF_PTREGS gap is a convention which helps the in-kernel + * unwinder reliably detect the end of the stack. + */ + .long init_thread_union + THREAD_SIZE - SIZEOF_PTREGS - \ + TOP_OF_KERNEL_STACK_PADDING; __INITRODATA int_msg: diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 1c5e5dba5704..b07cd27e33a5 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -66,13 +66,8 @@ startup_64: * tables and then reload them. */ - /* - * Setup stack for verify_cpu(). "-8" because initial_stack 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 + /* Set up the stack for verify_cpu(), similar to initial_stack below */ + leaq (__end_init_task - SIZEOF_PTREGS)(%rip), %rsp /* Sanitize CPU configuration */ call verify_cpu @@ -329,7 +324,11 @@ ENDPROC(start_cpu0) GLOBAL(initial_gs) .quad INIT_PER_CPU_VAR(irq_stack_union) GLOBAL(initial_stack) - .quad init_thread_union+THREAD_SIZE-8 + /* + * The SIZEOF_PTREGS gap is a convention which helps the in-kernel + * unwinder reliably detect the end of the stack. + */ + .quad init_thread_union + THREAD_SIZE - SIZEOF_PTREGS __FINITDATA bad_address: -- 2.30.2