Skip to content

[libos] Retain red zone area and FLAGS unmodified across syscall #355

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
Bonjourz wants to merge 1 commit into
base: master
Choose a base branch
from
Draft

[libos] Retain red zone area and FLAGS unmodified across syscall #355

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
35 changes: 25 additions & 10 deletions src/libos/src/entry/context_switch/switch_x86-64.S
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,10 @@ __switch_to_user:
pop %rcx
pop %rsp

// Skip the red zone aera (128 bytes according to x86_64 System V ABI)
// Use `lea` here since it does not modify FLAGS
lea -128(%rsp), %rsp

// Store RFLAGS since `cmp` operation may overwrite it
pushfq
push %rax
Expand All @@ -76,31 +80,34 @@ __switch_to_user:
pop %rax
popfq

lea 128(%rsp), %rsp
jmp *%gs:(TD_USER_RIP)
// This should never happen
ud2

update_pkru_at_switch_to_user:
pop %rax
popfq

sub $0x20, %rsp
mov %rax, (%rsp)
mov %rdx, 0x8(%rsp)
mov %rcx, 0x10(%rsp)
// Prepare temporary stack area for saving the %rdx, %rdx and return address
lea -3*8(%rsp), %rsp
mov %rdx, (%rsp)
mov %rcx, 8(%rsp)
mov %gs:(TD_USER_RIP), %rcx
mov %rcx, 0x18(%rsp)
mov %rcx, 2*8(%rsp)

xor %ecx, %ecx
xor %edx, %edx
mov $PKRU_USER, %eax
wrpkru

pop %rax
pop %rdx
pop %rcx
ret
// Skip the return address
lea 8(%rsp), %rsp

pop %rax
popfq
lea 128(%rsp), %rsp // Restore the %rsp

jmp *(-128-3*8)(%rsp)
// This should never happen
ud2

Expand Down Expand Up @@ -134,6 +141,11 @@ update_pkru_at_switch_to_user:
.global __syscall_entry_linux_pku_abi
.type __syscall_entry_linux_pku_abi, @function
__syscall_entry_linux_pku_abi:
// Skip the red zone aera (128 bytes according to x86_64 System V ABI)
// Use `lea` here since it does not modify FLAGS
lea -128(%rsp), %rsp

pushfq
pushq %rcx
pushq %rdx
pushq %rax
Expand All @@ -146,6 +158,9 @@ __syscall_entry_linux_pku_abi:
popq %rax
popq %rdx
popq %rcx
popfq

lea 128(%rsp), %rsp

.global __syscall_entry_linux_abi
.type __syscall_entry_linux_abi, @function
Expand Down