Setting the stack to PAGE_SIZE - 1 sets the stack to being 1-byte
aligned, which fails in usermode with alignment checks enabled (ie: with
flags cr0.am set and eflags.ac set). This was causing an #AC in
usermode.c when preparing to call the callback in run_in_user().
Aligning the stack fixes the issue.
For the purposes of fixing the #AC in usermode.c the stack has to be
aligned to at least an 8-byte boundary. Setting it to a page aligned
boundary ensures any stack alignment requirements are met as x86_64
stacks generally want to be 16-byte aligned.
Signed-off-by: Aaron Lewis <aaronlewis@xxxxxxxxxx>
---
x86/vmx.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/x86/vmx.c b/x86/vmx.c
index 6dc9a55..f4fbb94 100644
--- a/x86/vmx.c
+++ b/x86/vmx.c
@@ -42,7 +42,7 @@
u64 *bsp_vmxon_region;
struct vmcs *vmcs_root;
u32 vpid_cnt;
-void *guest_stack, *guest_syscall_stack;
+u64 guest_stack_top, guest_syscall_stack_top;
u32 ctrl_pin, ctrl_enter, ctrl_exit, ctrl_cpu[2];
struct regs regs;
@@ -1241,8 +1241,7 @@ static void init_vmcs_guest(void)
vmcs_write(GUEST_CR3, guest_cr3);
vmcs_write(GUEST_CR4, guest_cr4);
vmcs_write(GUEST_SYSENTER_CS, KERNEL_CS);
- vmcs_write(GUEST_SYSENTER_ESP,
- (u64)(guest_syscall_stack + PAGE_SIZE - 1));
+ vmcs_write(GUEST_SYSENTER_ESP, guest_syscall_stack_top);
vmcs_write(GUEST_SYSENTER_EIP, (u64)(&entry_sysenter));
vmcs_write(GUEST_DR7, 0);
vmcs_write(GUEST_EFER, rdmsr(MSR_EFER));
@@ -1292,7 +1291,7 @@ static void init_vmcs_guest(void)
/* 26.3.1.4 */
vmcs_write(GUEST_RIP, (u64)(&guest_entry));
- vmcs_write(GUEST_RSP, (u64)(guest_stack + PAGE_SIZE - 1));
+ vmcs_write(GUEST_RSP, guest_stack_top);
vmcs_write(GUEST_RFLAGS, X86_EFLAGS_FIXED);
/* 26.3.1.5 */
@@ -1388,8 +1387,8 @@ void init_vmx(u64 *vmxon_region)
static void alloc_bsp_vmx_pages(void)
{
bsp_vmxon_region = alloc_page();
- guest_stack = alloc_page();
- guest_syscall_stack = alloc_page();
+ guest_stack_top = (uintptr_t)alloc_page() + PAGE_SIZE;
+ guest_syscall_stack_top = (uintptr_t)alloc_page() + PAGE_SIZE;
vmcs_root = alloc_page();
}
--
2.34.1.173.g76aa8bc2d0-goog
