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authorThomas Gleixner <tglx@linutronix.de>2018-01-03 19:52:04 +0100
committerThomas Gleixner <tglx@linutronix.de>2018-01-03 23:19:32 +0100
commitd7732ba55c4b6a2da339bb12589c515830cfac2c (patch)
treecdf1579e8d02d42c408b607c4a7583038004f2a4 /arch
parent3ffdeb1a02be3086f1411a15c5b9c481fa28e21f (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
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/entry/entry_64_compat.S13
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.
*/