From ffae641f57476369b4d503402b37ebe489d23395 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 26 Jun 2020 10:21:13 -0700 Subject: [PATCH] x86/entry/64/compat: Fix Xen PV SYSENTER frame setup 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: 1c3e5d3f60e2 ("x86/entry: Make entry_64_compat.S objtool clean") Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Reviewed-by: Boris Ostrovsky Link: https://lkml.kernel.org/r/947880c41ade688ff4836f665d0c9fcaa9bd1201.1593191971.git.luto@kernel.org --- arch/x86/entry/entry_64_compat.S | 1 + arch/x86/xen/xen-asm_64.S | 20 ++++++++++++++++---- 2 files changed, 17 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 7b9d8150f652..381a6de7de9c 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -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 */ diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S index 5d252aaeade8..e1e1c7eafa60 100644 --- a/arch/x86/xen/xen-asm_64.S +++ b/arch/x86/xen/xen-asm_64.S @@ -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 */ -- 2.25.1