On 23/05/2024 1:33 pm, Alexandre Chartre wrote: > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S > index 11c9b8efdc4c..7fa04edc87e9 100644 > --- a/arch/x86/entry/entry_64_compat.S > +++ b/arch/x86/entry/entry_64_compat.S > @@ -91,7 +91,6 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) > > IBRS_ENTER > UNTRAIN_RET > - CLEAR_BRANCH_HISTORY > > /* > * SYSENTER doesn't filter flags, so we need to clear NT and AC > @@ -116,6 +115,12 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) > jnz .Lsysenter_fix_flags > .Lsysenter_flags_fixed: > > + /* > + * CLEAR_BRANCH_HISTORY can call other functions. It should be invoked > + * after making sure TF is cleared because single-step is ignored only > + * for instructions inside the entry_SYSENTER_compat function. > + */ > + CLEAR_BRANCH_HISTORY Exactly the same is true of UNTRAIN_RET, although it will only manifest in i386 builds running on AMD hardware (SYSENTER is #UD on AMD hardware in Long mode.) #DB is IST so does handle it's own speculation safety. It should be safe to move all the speculation safety logic in the sysenter handler to after .Lsysenter_flags_fixed:, I think? ~Andrew
