x86/entry/64/compat: Fix Xen PV SYSENTER frame setup (ffae641f) · Commits · 戴 / test

The SYSENTER frame setup was nonsense. It worked by accident because the normal code into which the Xen asm jumped (entry_SYSENTER_32/compat) threw away SP without touching the stack. entry_SYSENTER_compat was recently modified such that it relied on having a valid stack pointer, so now the Xen asm needs to invoke it with a valid stack. Fix it up like SYSCALL: use the Xen-provided frame and skip the bare metal prologue. Fixes: ("x86/entry: Make entry_64_compat.S objtool clean") Signed-off-by:

Andy Lutomirski <luto@kernel.org> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Reviewed-by:

Boris Ostrovsky <boris.ostrovsky@oracle.com> Link: https://lkml.kernel.org/r/947880c41ade688ff4836f665d0c9fcaa9bd1201.1593191971.git.luto@kernel.org

arch/x86/entry/entry_64_compat.S

+1 −0

Original line number	Diff line number	Diff line
		@@ -79,6 +79,7 @@ SYM_CODE_START(entry_SYSENTER_compat)
		pushfq /* pt_regs->flags (except IF = 0) */
		pushq $__USER32_CS /* pt_regs->cs */
		pushq $0 /* pt_regs->ip = 0 (placeholder) */
		SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
		pushq %rax /* pt_regs->orig_ax */
		pushq %rdi /* pt_regs->di */
		pushq %rsi /* pt_regs->si */

arch/x86/xen/xen-asm_64.S

+16 −4

Original line number	Diff line number	Diff line
		@@ -161,10 +161,22 @@ SYM_FUNC_END(xen_syscall32_target)

		/* 32-bit compat sysenter target */
		SYM_FUNC_START(xen_sysenter_target)
		mov 0*8(%rsp), %rcx
		mov 1*8(%rsp), %r11
		mov 5*8(%rsp), %rsp
		jmp entry_SYSENTER_compat
		/*
		* NB: Xen is polite and clears TF from EFLAGS for us. This means
		* that we don't need to guard against single step exceptions here.
		*/
		popq %rcx
		popq %r11

		/*
		* Neither Xen nor the kernel really knows what the old SS and
		* CS were. The kernel expects __USER32_DS and __USER32_CS, so
		* report those values even though Xen will guess its own values.
		*/
		movq $__USER32_DS, 4*8(%rsp)
		movq $__USER32_CS, 1*8(%rsp)

		jmp entry_SYSENTER_compat_after_hwframe
		SYM_FUNC_END(xen_sysenter_target)

		#else /* !CONFIG_IA32_EMULATION */

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