Messages in this thread | ![/](/images/icornerl.gif) | | From | Lai Jiangshan <> | Date | Fri, 29 Apr 2022 19:45:43 +0800 | Subject | Re: [PATCH V6 6/8] x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS |
| |
On Fri, Apr 29, 2022 at 5:56 PM Borislav Petkov <bp@alien8.de> wrote: > > On Thu, Apr 21, 2022 at 10:10:53PM +0800, Lai Jiangshan wrote: > > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S > > index 4fdb007cddbd..c5aeb0819707 100644 > > --- a/arch/x86/entry/entry_64_compat.S > > +++ b/arch/x86/entry/entry_64_compat.S > > @@ -50,7 +50,7 @@ SYM_CODE_START(entry_SYSENTER_compat) > > UNWIND_HINT_EMPTY > > ENDBR > > /* Interrupts are off on entry. */ > > - SWAPGS > > + swapgs > > > > pushq %rax > > SWITCH_TO_KERNEL_CR3 scratch_reg=%rax > > I'm not sure about this: why can't XENPV do a 32-bit syscall through the vdso? > > Also, looking at this, Jürgen, it looks kinda spaghetti to me: > > entry_SYSENTER_compat > > ... > > /* XEN PV guests always use IRET path */ > ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ > "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV > > > then at that swapgs_restore_regs_and_return_to_usermode label: > > #ifdef CONFIG_XEN_PV > ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV > #endif > > > Can we simply jump directly to xenpv_restore_regs_and_return_to_usermode > from entry_SYSENTER_compat or is that CONFIG_DEBUG_ENTRY chunk there > needed?
Hello
Adding ALTERNATIVE in swapgs_restore_regs_and_return_to_usermode() results a simpler patch which is better served as a bug fix:
https://lore.kernel.org/lkml/163861832551.11128.1645285137833652414.tip-bot2@tip-bot2/
which is also your suggestion:
https://lore.kernel.org/lkml/YYD9ohN2Zcy4EdMb@zn.tnic/
While the original patch has sprinkled all those ALTERNATIVE calls everywhere:
https://lore.kernel.org/lkml/20211026141420.17138-5-jiangshanlai@gmail.com/
And this original version has a SYM_L_WEAK placeholder which is objected to by some people.
Thanks Lai
| ![\](/images/icornerr.gif) |