diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2018-01-03 19:52:04 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-01-03 23:19:32 +0100 |
| commit | d7732ba55c4b6a2da339bb12589c515830cfac2c (patch) | |
| tree | cdf1579e8d02d42c408b607c4a7583038004f2a4 | |
| parent | 3ffdeb1a02be3086f1411a15c5b9c481fa28e21f (diff) | |
x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat()
The preparation for PTI which added CR3 switching to the entry code
misplaced the CR3 switch in entry_SYSCALL_compat().
With PTI enabled the entry code tries to access a per cpu variable after
switching to kernel GS. This fails because that variable is not mapped to
user space. This results in a double fault and in the worst case a kernel
crash.
Move the switch ahead of the access and clobber RSP which has been saved
already.
Fixes: 8a09317b895f ("x86/mm/pti: Prepare the x86/entry assembly code for entry/exit CR3 switching")
Reported-by: Lars Wendler <wendler.lars@web.de>
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>,
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Cc: Peter Zijlstra <peterz@infradead.org>,
Cc: Greg KH <gregkh@linuxfoundation.org>, ,
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Cc: Juergen Gross <jgross@suse.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801031949200.1957@nanos
| -rw-r--r-- | arch/x86/entry/entry_64_compat.S | 13 |
1 files changed, 6 insertions, 7 deletions
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 40f17009ec20..98d5358e4041 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat) /* Interrupts are off on entry. */ swapgs - /* Stash user ESP and switch to the kernel stack. */ + /* Stash user ESP */ movl %esp, %r8d + + /* Use %rsp as scratch reg. User ESP is stashed in r8 */ + SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp + + /* Switch to the kernel stack */ movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp /* Construct struct pt_regs on stack */ @@ -220,12 +225,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe) pushq $0 /* pt_regs->r15 = 0 */ /* - * We just saved %rdi so it is safe to clobber. It is not - * preserved during the C calls inside TRACE_IRQS_OFF anyway. - */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi - - /* * User mode is traced as though IRQs are on, and SYSENTER * turned them off. */ |