From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> commit 2e2e5143d4868163d6756c8c6a4d28cbfa5245e5 upstream. Opportunistic SYSEXIT executes VERW to clear CPU buffers after user EFLAGS are restored. This can clobber user EFLAGS.ZF. Move CLEAR_CPU_BUFFERS before the user EFLAGS are restored. This ensures that the user EFLAGS.ZF is not clobbered. Closes: https://lore.kernel.org/lkml/yVXwe8gvgmPADpRB6lXlicS2fcHoV5OHHxyuFbB_MEleRPD7-KhGe5VtORejtPe-KCkT8Uhcg5d7-IBw4Ojb4H7z5LQxoZylSmJ8KNL3A8o=@protonmail.com/ Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition") Reported-by: Jari Ruusu <jariruusu@xxxxxxxxxxxxxx> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc:stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-1-1de0daca2d42%40linux.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/entry/entry_32.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -939,6 +939,8 @@ SYM_FUNC_START(entry_SYSENTER_32) /* Now ready to switch the cr3 */ SWITCH_TO_USER_CR3 scratch_reg=%eax + /* Clobbers ZF */ + CLEAR_CPU_BUFFERS /* * Restore all flags except IF. (We restore IF separately because @@ -949,7 +951,6 @@ SYM_FUNC_START(entry_SYSENTER_32) BUG_IF_WRONG_CR3 no_user_check=1 popfl popl %eax - CLEAR_CPU_BUFFERS /* * Return back to the vDSO, which will pop ecx and edx. Patches currently in stable-queue which might be from pawan.kumar.gupta@xxxxxxxxxxxxxxx are queue-5.10/x86-entry_32-do-not-clobber-user-eflags.zf.patch queue-5.10/x86-entry_32-clear-cpu-buffers-after-register-restore-in-nmi-return.patch
