x86/entry/64: Really create an error-entry-from-usermode code path (cb6f64ed) · Commits · 戴 / test

In ("x86/asm/entry/64: Disentangle error_entry/exit gsbase/ebx/usermode code"), I arranged the code slightly wrong -- IRET faults would skip the code path that was intended to execute on all error entries from user mode. Fix it up. While we're at it, make all the labels in error_entry local. This does not fix a bug, but we'll need it, and it slightly shrinks the code. Signed-off-by:

Andy Lutomirski <luto@kernel.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Denys Vlasenko <vda.linux@googlemail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/91e17891e49fa3d61357eadc451529ad48143ee1.1435952415.git.luto@kernel.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_64.S

+16 −12

Original line number	Diff line number	Diff line
		@@ -1143,12 +1143,17 @@ ENTRY(error_entry)
		SAVE_EXTRA_REGS 8
		xorl %ebx, %ebx
		testb $3, CS+8(%rsp)
		jz error_kernelspace
		jz .Lerror_kernelspace

		/* We entered from user mode */
		.Lerror_entry_from_usermode_swapgs:
		/*
		* We entered from user mode or we're pretending to have entered
		* from user mode due to an IRET fault.
		*/
		SWAPGS

		error_entry_done:
		.Lerror_entry_from_usermode_after_swapgs:
		.Lerror_entry_done:
		TRACE_IRQS_OFF
		ret

		@@ -1158,31 +1163,30 @@ error_entry_done:
		* truncated RIP for IRET exceptions returning to compat mode. Check
		* for these here too.
		*/
		error_kernelspace:
		.Lerror_kernelspace:
		incl %ebx
		leaq native_irq_return_iret(%rip), %rcx
		cmpq %rcx, RIP+8(%rsp)
		je error_bad_iret
		je .Lerror_bad_iret
		movl %ecx, %eax /* zero extend */
		cmpq %rax, RIP+8(%rsp)
		je bstep_iret
		je .Lbstep_iret
		cmpq $gs_change, RIP+8(%rsp)
		jne error_entry_done
		jne .Lerror_entry_done

		/*
		* hack: gs_change can fail with user gsbase. If this happens, fix up
		* gsbase and proceed. We'll fix up the exception and land in
		* gs_change's error handler with kernel gsbase.
		*/
		SWAPGS
		jmp error_entry_done
		jmp .Lerror_entry_from_usermode_swapgs

		bstep_iret:
		.Lbstep_iret:
		/* Fix truncated RIP */
		movq %rcx, RIP+8(%rsp)
		/* fall through */

		error_bad_iret:
		.Lerror_bad_iret:
		/*
		* We came from an IRET to user mode, so we have user gsbase.
		* Switch to kernel gsbase:
		@@ -1198,7 +1202,7 @@ error_bad_iret:
		call fixup_bad_iret
		mov %rax, %rsp
		decl %ebx
		jmp error_entry_done
		jmp .Lerror_entry_from_usermode_after_swapgs
		END(error_entry)

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