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Message-ID: <CAMzpN2gF7QxDbVG-6ad3Qarcn1N_JT5tit9CMvQL95LQGeZivA@mail.gmail.com>
Date: Tue, 18 Jul 2017 22:49:15 -0400
From: Brian Gerst <brgerst@...il.com>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>, "David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
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Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC 06/22] kvm: Adapt assembly for PIE support
On Tue, Jul 18, 2017 at 6:33 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
> Change the assembly code to use only relative references of symbols for the
> kernel to be PIE compatible. The new __ASM_GET_PTR_PRE macro is used to
> get the address of a symbol on both 32 and 64-bit with PIE support.
>
> Position Independent Executable (PIE) support will allow to extended the
> KASLR randomization range below the -2G memory limit.
>
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---
> arch/x86/include/asm/kvm_host.h | 6 ++++--
> arch/x86/kernel/kvm.c | 6 ++++--
> arch/x86/kvm/svm.c | 4 ++--
> 3 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 87ac4fba6d8e..3041201a3aeb 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1352,9 +1352,11 @@ asmlinkage void kvm_spurious_fault(void);
> ".pushsection .fixup, \"ax\" \n" \
> "667: \n\t" \
> cleanup_insn "\n\t" \
> - "cmpb $0, kvm_rebooting \n\t" \
> + "cmpb $0, kvm_rebooting" __ASM_SEL(,(%%rip)) " \n\t" \
> "jne 668b \n\t" \
> - __ASM_SIZE(push) " $666b \n\t" \
> + __ASM_SIZE(push) "%%" _ASM_AX " \n\t" \
> + __ASM_GET_PTR_PRE(666b) "%%" _ASM_AX "\n\t" \
> + "xchg %%" _ASM_AX ", (%%" _ASM_SP ") \n\t" \
> "call kvm_spurious_fault \n\t" \
> ".popsection \n\t" \
> _ASM_EXTABLE(666b, 667b)
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 71c17a5be983..53b8ad162589 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -618,8 +618,10 @@ asm(
> ".global __raw_callee_save___kvm_vcpu_is_preempted;"
> ".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
> "__raw_callee_save___kvm_vcpu_is_preempted:"
> -"movq __per_cpu_offset(,%rdi,8), %rax;"
> -"cmpb $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax);"
> +"leaq __per_cpu_offset(%rip), %rax;"
> +"movq (%rax,%rdi,8), %rax;"
> +"addq " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rip), %rax;"
This doesn't look right. It's accessing a per-cpu variable. The
per-cpu section is an absolute, zero-based section and not subject to
relocation.
> +"cmpb $0, (%rax);
> "setne %al;"
> "ret;"
> ".popsection");
--
Brian Gerst
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