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Date: Tue, 02 Dec 2014 13:20:40 -0800
From: Kamal Mostafa <kamal@...onical.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
stable <stable@...r.kernel.org>, kernel-team@...ts.ubuntu.com,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3.13.y-ckt 119/121] x86_64, traps: Fix the espfix64 #DF
fixup and rewrite it in C
On Tue, 2014-12-02 at 11:34 -0800, Andy Lutomirski wrote:
> As before, this and "Reword bad_iret" may want to wait a week or two.
> They're not very urgent.
Ok, I'll defer those two until the next 3.13-stable cycle.
Thanks Andy,
-Kamal
> --Andy
>
> On Tue, Dec 2, 2014 at 11:19 AM, Kamal Mostafa <kamal@...onical.com> wrote:
> > 3.13.11-ckt12 -stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Andy Lutomirski <luto@...capital.net>
> >
> > commit af726f21ed8af2cdaa4e93098dc211521218ae65 upstream.
> >
> > There's nothing special enough about the espfix64 double fault fixup to
> > justify writing it in assembly. Move it to C.
> >
> > This also fixes a bug: if the double fault came from an IST stack, the
> > old asm code would return to a partially uninitialized stack frame.
> >
> > Fixes: 3891a04aafd668686239349ea58f3314ea2af86b
> > Signed-off-by: Andy Lutomirski <luto@...capital.net>
> > Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > [ kamal: backport to 3.13-stable: context ]
> > Signed-off-by: Kamal Mostafa <kamal@...onical.com>
> > ---
> > arch/x86/kernel/entry_64.S | 34 ++--------------------------------
> > arch/x86/kernel/traps.c | 24 ++++++++++++++++++++++++
> > 2 files changed, 26 insertions(+), 32 deletions(-)
> >
> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> > index 03cd2a8..2bb5032 100644
> > --- a/arch/x86/kernel/entry_64.S
> > +++ b/arch/x86/kernel/entry_64.S
> > @@ -1053,6 +1053,7 @@ ENTRY(native_iret)
> > jnz native_irq_return_ldt
> > #endif
> >
> > +.global native_irq_return_iret
> > native_irq_return_iret:
> > iretq
> > _ASM_EXTABLE(native_irq_return_iret, bad_iret)
> > @@ -1147,37 +1148,6 @@ ENTRY(retint_kernel)
> > CFI_ENDPROC
> > END(common_interrupt)
> >
> > - /*
> > - * If IRET takes a fault on the espfix stack, then we
> > - * end up promoting it to a doublefault. In that case,
> > - * modify the stack to make it look like we just entered
> > - * the #GP handler from user space, similar to bad_iret.
> > - */
> > -#ifdef CONFIG_X86_ESPFIX64
> > - ALIGN
> > -__do_double_fault:
> > - XCPT_FRAME 1 RDI+8
> > - movq RSP(%rdi),%rax /* Trap on the espfix stack? */
> > - sarq $PGDIR_SHIFT,%rax
> > - cmpl $ESPFIX_PGD_ENTRY,%eax
> > - jne do_double_fault /* No, just deliver the fault */
> > - cmpl $__KERNEL_CS,CS(%rdi)
> > - jne do_double_fault
> > - movq RIP(%rdi),%rax
> > - cmpq $native_irq_return_iret,%rax
> > - jne do_double_fault /* This shouldn't happen... */
> > - movq PER_CPU_VAR(kernel_stack),%rax
> > - subq $(6*8-KERNEL_STACK_OFFSET),%rax /* Reset to original stack */
> > - movq %rax,RSP(%rdi)
> > - movq $0,(%rax) /* Missing (lost) #GP error code */
> > - movq $general_protection,RIP(%rdi)
> > - retq
> > - CFI_ENDPROC
> > -END(__do_double_fault)
> > -#else
> > -# define __do_double_fault do_double_fault
> > -#endif
> > -
> > /*
> > * End of kprobes section
> > */
> > @@ -1379,7 +1349,7 @@ zeroentry overflow do_overflow
> > zeroentry bounds do_bounds
> > zeroentry invalid_op do_invalid_op
> > zeroentry device_not_available do_device_not_available
> > -paranoiderrorentry double_fault __do_double_fault
> > +paranoiderrorentry double_fault do_double_fault
> > zeroentry coprocessor_segment_overrun do_coprocessor_segment_overrun
> > errorentry invalid_TSS do_invalid_TSS
> > errorentry segment_not_present do_segment_not_present
> > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> > index b857ed8..e5b2976 100644
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -248,6 +248,30 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
> > static const char str[] = "double fault";
> > struct task_struct *tsk = current;
> >
> > +#ifdef CONFIG_X86_ESPFIX64
> > + extern unsigned char native_irq_return_iret[];
> > +
> > + /*
> > + * If IRET takes a non-IST fault on the espfix64 stack, then we
> > + * end up promoting it to a doublefault. In that case, modify
> > + * the stack to make it look like we just entered the #GP
> > + * handler from user space, similar to bad_iret.
> > + */
> > + if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
> > + regs->cs == __KERNEL_CS &&
> > + regs->ip == (unsigned long)native_irq_return_iret)
> > + {
> > + struct pt_regs *normal_regs = task_pt_regs(current);
> > +
> > + /* Fake a #GP(0) from userspace. */
> > + memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
> > + normal_regs->orig_ax = 0; /* Missing (lost) #GP error code */
> > + regs->ip = (unsigned long)general_protection;
> > + regs->sp = (unsigned long)&normal_regs->orig_ax;
> > + return;
> > + }
> > +#endif
> > +
> > exception_enter();
> > /* Return not checked because double check cannot be ignored */
> > notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
> > --
> > 1.9.1
> >
>
>
>
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