From 7bf36bbc5e0c09271f9efe22162f8cc3f8ebd3d2 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 7 Apr 2006 19:50:00 +0200 Subject: [PATCH] [PATCH] x86_64: When user could have changed RIP always force IRET Intel EM64T CPUs handle uncanonical return addresses differently from AMD CPUs. The exception is reported in the SYSRET, not the next instruction. This leads to the kernel exception handler running on the user stack with the wrong GS because the kernel didn't expect exceptions on this instruction. This version of the patch has the teething problems that plagued an earlier version fixed. This is CVE-2006-0744 Thanks to Ernie Petrides and Asit B. Mallick for analysis and initial patches. Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- arch/x86_64/kernel/entry.S | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S index 10ec27b607f..c946e4fe67a 100644 --- a/arch/x86_64/kernel/entry.S +++ b/arch/x86_64/kernel/entry.S @@ -180,6 +180,10 @@ rff_trace: * * XXX if we had a free scratch register we could save the RSP into the stack frame * and report it properly in ps. Unfortunately we haven't. + * + * When user can change the frames always force IRET. That is because + * it deals with uncanonical addresses better. SYSRET has trouble + * with them due to bugs in both AMD and Intel CPUs. */ ENTRY(system_call) @@ -254,7 +258,10 @@ sysret_signal: xorl %esi,%esi # oldset -> arg2 call ptregscall_common 1: movl $_TIF_NEED_RESCHED,%edi - jmp sysret_check + /* Use IRET because user could have changed frame. This + works because ptregscall_common has called FIXUP_TOP_OF_STACK. */ + cli + jmp int_with_check badsys: movq $-ENOSYS,RAX-ARGOFFSET(%rsp) @@ -280,7 +287,8 @@ tracesys: call syscall_trace_leave RESTORE_TOP_OF_STACK %rbx RESTORE_REST - jmp ret_from_sys_call + /* Use IRET because user could have changed frame */ + jmp int_ret_from_sys_call CFI_ENDPROC /* -- 2.41.0