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Date: Tue, 2 Dec 2014 11:34:09 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Kamal Mostafa <kamal@...onical.com>
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
As before, this and "Reword bad_iret" may want to wait a week or two.
They're not very urgent.
--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
>
--
Andy Lutomirski
AMA Capital Management, LLC
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