From 04f4f954b69526d7af8ffb8e5780f08b8a6cda2d Mon Sep 17 00:00:00 2001 From: Jan Kiszka Date: Mon, 15 Oct 2018 16:09:29 +0200 Subject: x86/entry/32: Clear the CS high bits Even if not on an entry stack, the CS's high bits must be initialized because they are unconditionally evaluated in PARANOID_EXIT_TO_KERNEL_MODE. Failing to do so broke the boot on Galileo Gen2 and IOT2000 boards. [ bp: Make the commit message tone passive and impartial. ] Fixes: b92a165df17e ("x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack") Signed-off-by: Jan Kiszka Signed-off-by: Borislav Petkov Reviewed-by: Joerg Roedel Acked-by: Joerg Roedel CC: "H. Peter Anvin" CC: Andrea Arcangeli CC: Andy Lutomirski CC: Boris Ostrovsky CC: Brian Gerst CC: Dave Hansen CC: David Laight CC: Denys Vlasenko CC: Eduardo Valentin CC: Greg KH CC: Ingo Molnar CC: Jiri Kosina CC: Josh Poimboeuf CC: Juergen Gross CC: Linus Torvalds CC: Peter Zijlstra CC: Thomas Gleixner CC: Will Deacon CC: aliguori@amazon.com CC: daniel.gruss@iaik.tugraz.at CC: hughd@google.com CC: keescook@google.com CC: linux-mm CC: x86-ml Link: http://lkml.kernel.org/r/f271c747-1714-5a5b-a71f-ae189a093b8d@siemens.com Signed-off-by: Ingo Molnar --- arch/x86/entry/entry_32.S | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'arch/x86/entry/entry_32.S') diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 2767c625a52c..fbbf1ba57ec6 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -389,6 +389,13 @@ * that register for the time this macro runs */ + /* + * The high bits of the CS dword (__csh) are used for + * CS_FROM_ENTRY_STACK and CS_FROM_USER_CR3. Clear them in case + * hardware didn't do this for us. + */ + andl $(0x0000ffff), PT_CS(%esp) + /* Are we on the entry stack? Bail out if not! */ movl PER_CPU_VAR(cpu_entry_area), %ecx addl $CPU_ENTRY_AREA_entry_stack + SIZEOF_entry_stack, %ecx @@ -407,12 +414,6 @@ /* Load top of task-stack into %edi */ movl TSS_entry2task_stack(%edi), %edi - /* - * Clear unused upper bits of the dword containing the word-sized CS - * slot in pt_regs in case hardware didn't clear it for us. - */ - andl $(0x0000ffff), PT_CS(%esp) - /* Special case - entry from kernel mode via entry stack */ #ifdef CONFIG_VM86 movl PT_EFLAGS(%esp), %ecx # mix EFLAGS and CS -- cgit v1.2.3