The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 2e2e5143d4868163d6756c8c6a4d28cbfa5245e5 Gitweb: https://git.kernel.org/tip/2e2e5143d4868163d6756c8c6a4d28cbfa5245e5 Author: Pawan Gupta pawan.kumar.gupta@linux.intel.com AuthorDate: Wed, 25 Sep 2024 15:25:38 -07:00 Committer: Dave Hansen dave.hansen@linux.intel.com CommitterDate: Tue, 08 Oct 2024 15:16:28 -07:00

x86/entry_32: Do not clobber user EFLAGS.ZF

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_MEleRPD... Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition") Reported-by: Jari Ruusu jariruusu@protonmail.com Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-1-1de0daca2d42%40lin... --- arch/x86/entry/entry_32.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index d3a814e..9ad6cd8 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -871,6 +871,8 @@ 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 @@ -881,7 +883,6 @@ 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.