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Date: Tue, 15 Jul 2014 10:22:12 -0700 From: Andy Lutomirski <luto@...capital.net> To: Boris Ostrovsky <boris.ostrovsky@...cle.com> Cc: "H. Peter Anvin" <hpa@...or.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> Subject: Re: [RFC PATCH] x86_64,entry,xen: Do not invoke espfix64 on Xen On Tue, Jul 15, 2014 at 10:19 AM, Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote: > On 07/15/2014 12:23 PM, Andy Lutomirski wrote: >> >> This moves the espfix64 logic into native_iret. To make this work, >> it gets rid of the native patch for INTERRUPT_RETURN: >> INTERRUPT_RETURN on native kernels is now 'jmp native_iret'. >> >> This changes the 16-bit SS behavior on Xen from OOPSing to leaking >> some bits of the Xen hypervisor's RSP (I think). >> >> Signed-off-by: Andy Lutomirski <luto@...capital.net> >> --- >> >> I just pushed this to kernel.org, so the kbuild robot should be pounding >> on it soon. It passes all my tests on bare metal, and it fails them >> without crashing on Xen. >> >> It's not exactly beautiful, but I think it's an improvement. >> >> arch/x86/include/asm/irqflags.h | 2 +- >> arch/x86/kernel/entry_64.S | 28 ++++++++++------------------ >> arch/x86/kernel/paravirt_patch_64.c | 2 -- >> 3 files changed, 11 insertions(+), 21 deletions(-) >> >> diff --git a/arch/x86/include/asm/irqflags.h >> b/arch/x86/include/asm/irqflags.h >> index bba3cf8..0a8b519 100644 >> --- a/arch/x86/include/asm/irqflags.h >> +++ b/arch/x86/include/asm/irqflags.h >> @@ -129,7 +129,7 @@ static inline notrace unsigned long >> arch_local_irq_save(void) >> #define PARAVIRT_ADJUST_EXCEPTION_FRAME /* */ >> -#define INTERRUPT_RETURN iretq >> +#define INTERRUPT_RETURN jmp native_iret >> #define USERGS_SYSRET64 \ >> swapgs; \ >> sysretq; >> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S >> index b25ca96..c844f08 100644 >> --- a/arch/x86/kernel/entry_64.S >> +++ b/arch/x86/kernel/entry_64.S >> @@ -830,27 +830,24 @@ restore_args: >> RESTORE_ARGS 1,8,1 >> irq_return: >> + INTERRUPT_RETURN >> + >> +ENTRY(native_iret) >> /* >> * Are we returning to a stack segment from the LDT? Note: in >> * 64-bit mode SS:RSP on the exception stack is always valid. >> */ >> #ifdef CONFIG_X86_ESPFIX64 >> testb $4,(SS-RIP)(%rsp) >> - jnz irq_return_ldt >> + jnz native_irq_return_ldt >> #endif >> -irq_return_iret: >> - INTERRUPT_RETURN >> - _ASM_EXTABLE(irq_return_iret, bad_iret) >> - >> -#ifdef CONFIG_PARAVIRT >> -ENTRY(native_iret) >> +native_irq_return_iret: >> iretq >> - _ASM_EXTABLE(native_iret, bad_iret) >> -#endif >> + _ASM_EXTABLE(native_irq_return_iret, bad_iret) >> #ifdef CONFIG_X86_ESPFIX64 >> -irq_return_ldt: >> +native_irq_return_ldt: >> pushq_cfi %rax >> pushq_cfi %rdi >> SWAPGS >> @@ -872,7 +869,7 @@ irq_return_ldt: >> SWAPGS >> movq %rax,%rsp >> popq_cfi %rax >> - jmp irq_return_iret >> + jmp native_irq_return_iret >> #endif >> .section .fixup,"ax" >> @@ -956,13 +953,8 @@ __do_double_fault: >> cmpl $__KERNEL_CS,CS(%rdi) >> jne do_double_fault >> movq RIP(%rdi),%rax >> - cmpq $irq_return_iret,%rax >> -#ifdef CONFIG_PARAVIRT >> - je 1f >> - cmpq $native_iret,%rax >> -#endif >> + cmpq $native_irq_return_iret,%rax >> jne do_double_fault /* This shouldn't happen... */ >> -1: >> movq PER_CPU_VAR(kernel_stack),%rax >> subq $(6*8-KERNEL_STACK_OFFSET),%rax /* Reset to original stack >> */ >> movq %rax,RSP(%rdi) >> @@ -1428,7 +1420,7 @@ error_sti: >> */ >> error_kernelspace: >> incl %ebx >> - leaq irq_return_iret(%rip),%rcx >> + leaq native_irq_return_iret(%rip),%rcx >> cmpq %rcx,RIP+8(%rsp) >> je error_swapgs >> movl %ecx,%eax /* zero extend */ >> diff --git a/arch/x86/kernel/paravirt_patch_64.c >> b/arch/x86/kernel/paravirt_patch_64.c >> index 3f08f34..a1da673 100644 >> --- a/arch/x86/kernel/paravirt_patch_64.c >> +++ b/arch/x86/kernel/paravirt_patch_64.c >> @@ -6,7 +6,6 @@ DEF_NATIVE(pv_irq_ops, irq_disable, "cli"); >> DEF_NATIVE(pv_irq_ops, irq_enable, "sti"); >> DEF_NATIVE(pv_irq_ops, restore_fl, "pushq %rdi; popfq"); >> DEF_NATIVE(pv_irq_ops, save_fl, "pushfq; popq %rax"); >> -DEF_NATIVE(pv_cpu_ops, iret, "iretq"); >> DEF_NATIVE(pv_mmu_ops, read_cr2, "movq %cr2, %rax"); >> DEF_NATIVE(pv_mmu_ops, read_cr3, "movq %cr3, %rax"); >> DEF_NATIVE(pv_mmu_ops, write_cr3, "movq %rdi, %cr3"); >> @@ -50,7 +49,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf, >> PATCH_SITE(pv_irq_ops, save_fl); >> PATCH_SITE(pv_irq_ops, irq_enable); >> PATCH_SITE(pv_irq_ops, irq_disable); >> - PATCH_SITE(pv_cpu_ops, iret); > > > > Does this mean that we are no longer patching IRET with a jump to a > hypercall? > IIUC this means that, on native, we are no longer patching INTERRUPT_RETURN with an "iretq" instruction, so INTERRUPT_RETURN will remain a "jmp native_iret". I'm not sure why this patch was there in the first place. On Xen, it should still get patched with the hypercall (although someone should verify this). --Andy > -boris > > > >> PATCH_SITE(pv_cpu_ops, irq_enable_sysexit); >> PATCH_SITE(pv_cpu_ops, usergs_sysret32); >> PATCH_SITE(pv_cpu_ops, usergs_sysret64); > > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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