Commit 8264e855 authored by Ackerley Tng's avatar Ackerley Tng Committed by Sean Christopherson
Browse files

KVM: selftests: Adjust VM's initial stack address to align with SysV ABI spec 



Align the guest stack to match calling sequence requirements in
section "The Stack Frame" of the System V ABI AMD64 Architecture
Processor Supplement, which requires the value (%rsp + 8), NOT %rsp,
to be a multiple of 16 when control is transferred to the function
entry point. I.e. in a normal function call, %rsp needs to be 16-byte
aligned _before_ CALL, not after.

This fixes unexpected #GPs in guest code when the compiler uses SSE
instructions, e.g. to initialize memory, as many SSE instructions
require memory operands (including those on the stack) to be
16-byte-aligned.

Signed-off-by: default avatarAckerley Tng <ackerleytng@google.com>
Link: https://lore.kernel.org/r/20230227180601.104318-1-ackerleytng@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 5b1abc28

tools/testing/selftests/kvm/lib/x86_64/processor.c

+17 −1
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
 * Copyright (C) 2018, Google LLC.

 */



#include "linux/bitmap.h"

#include "test_util.h"

#include "kvm_util.h"

#include "processor.h"
@@ -573,6 +574,21 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id, 
				       DEFAULT_GUEST_STACK_VADDR_MIN,

				       MEM_REGION_DATA);



	stack_vaddr += DEFAULT_STACK_PGS * getpagesize();



	/*

	 * Align stack to match calling sequence requirements in section "The

	 * Stack Frame" of the System V ABI AMD64 Architecture Processor

	 * Supplement, which requires the value (%rsp + 8) to be a multiple of

	 * 16 when control is transferred to the function entry point.

	 *

	 * If this code is ever used to launch a vCPU with 32-bit entry point it

	 * may need to subtract 4 bytes instead of 8 bytes.

	 */

	TEST_ASSERT(IS_ALIGNED(stack_vaddr, PAGE_SIZE),

		    "__vm_vaddr_alloc() did not provide a page-aligned address");

	stack_vaddr -= 8;



	vcpu = __vm_vcpu_add(vm, vcpu_id);

	vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());

	vcpu_setup(vm, vcpu);
@@ -580,7 +596,7 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id, 
	/* Setup guest general purpose registers */

	vcpu_regs_get(vcpu, &regs);

	regs.rflags = regs.rflags | 0x2;

	regs.rsp = stack_vaddr + (DEFAULT_STACK_PGS * getpagesize());

	regs.rsp = stack_vaddr;

	regs.rip = (unsigned long) guest_code;

	vcpu_regs_set(vcpu, &regs);