[PATCH] x86_64: When user could have changed RIP always force IRET (7bf36bbc) · Commits · 戴 / test

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 <ak@suse.de> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/entry.S

+10 −2

Original line number	Diff line number	Diff line
		@@ -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

		/*

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