5.10-stable review patch. If anyone has any objections, please let me know.
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From: Pawan Gupta pawan.kumar.gupta@linux.intel.com
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_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... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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.