Syscall entry/exit register save / restore (general purpose and FPU/MMX/SSE/AVX) #9
Assignees
Labels
Comments
kuqin12
added a commit
that referenced
this issue
Aug 20, 2022
…MX/SSE/AVX) (#20) Bug Description: SyscallCenter implemented in SysCallEntry.nasm is called as the supervisor entry point when user space issues a SYSCALL instruction. This function is responsible for proper setup, calling the dispatcher, and then returning to user space properly. Except, it doesn't seem to restore all registers. It restores a subset of the general purpose registers (r11, rbx, rdi, r12, rsi, r9, r8, rdx, rbp rcx and rsp), clearly leaving out r10, r13, r14, and r15. If the dispatcher uses any of these registers, they would get returned to user space. In addition to the general purpose registers, it doesn't seem to restore any of the FPU/MMX/SSE/AVX registers. Optimizing compilers tend to use the SIMD registers and instructions for things like memcpy(). Fix: In the syscall interface: - Adding saving/restoring all general purpose registers. - Saving/restoring MMX/SSE/FPU registers with FXSAVE and FXSTOR. - AVX operations are prohibited by not enabling OSXSAVE in CR4. The instructions addition is measured to have <100ms slowdown for 1M syscall calls. fixes #9
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
SyscallCenter implemented in SysCallEntry.nasm is called as the supervisor entry point when user space issues a SYSCALL instruction. This function is responsible for proper setup, calling the dispatcher, and then returning to user space properly.
Except, it doesn't seem to restore all registers. It restores a subset of the general-purpose registers (r11, rbx, rdi, r12, rsi, r9, r8, rdx, rbp rcx and rsp), clearly leaving out r10, r13, r14, and r15. If the dispatcher uses any of these registers, they would get returned to user space.
In addition to the general-purpose registers, it doesn't seem to restore any of the FPU/MMX/SSE/AVX registers. Optimizing compilers tend to use the SIMD registers and instructions for things like memcpy().
Fix Recommendation:
Consider saving/restoring all general-purpose registers.
Acknowledgement:
Thanks to @iljavs for reporting this issue.
The text was updated successfully, but these errors were encountered: