From: Thomas Garnier Subject: Re: [RFC 06/22] kvm: Adapt assembly for PIE support Date: Wed, 19 Jul 2017 08:40:14 -0700 Message-ID: References: <20170718223333.110371-1-thgarnie@google.com> <20170718223333.110371-7-thgarnie@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Herbert Xu , "David S . Miller" , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Peter Zijlstra , Josh Poimboeuf , Arnd Bergmann , Matthias Kaehlcke , Boris Ostrovsky , Juergen Gross , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Joerg Roedel , Andy Lutomirski , Borislav Petkov , "Kirill A . Shutemov" , Borislav Petkov , Christian Borntraeger , "Rafael J . Wysocki" , Len Brown , Pavel Machek , Tejun Heo , Chris To: Brian Gerst Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: List-Id: linux-crypto.vger.kernel.org On Tue, Jul 18, 2017 at 7:49 PM, Brian Gerst wrote: > On Tue, Jul 18, 2017 at 6:33 PM, Thomas Garnier 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 >> --- >> 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. > PIE does not respect the zero-based section, it tries to have everything relative. Patch 16/22 also adapt per-cpu to work with PIE (while keeping the zero absolute design by default). >> +"cmpb $0, (%rax); >> "setne %al;" >> "ret;" >> ".popsection"); > > -- > Brian Gerst -- Thomas