From 114e31ccf4ab4e787340032f3630638ea36b0b71 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Wed, 15 Jun 2016 18:32:14 +0100 Subject: [PATCH] x86/entry: Avoid SMAP violation in compat_create_bounce_frame() A 32bit guest kernel might be running on user mappings. compat_create_bounce_frame() must whitelist its guest accesses to avoid risking a SMAP violation. For both variants of create_bounce_frame(), re-blacklist user accesses if execution exits via an exception table redirection. This is XSA-183 Signed-off-by: Andrew Cooper Reviewed-by: George Dunlap --- xen/arch/x86/x86_64/compat/entry.S | 3 +++ xen/arch/x86/x86_64/entry.S | 1 + 2 files changed, 4 insertions(+) diff --git a/xen/arch/x86/x86_64/compat/entry.S b/xen/arch/x86/x86_64/compat/entry.S index 0e3db7c..89c1e19 100644 --- a/xen/arch/x86/x86_64/compat/entry.S +++ b/xen/arch/x86/x86_64/compat/entry.S @@ -351,6 +351,7 @@ compat_create_bounce_frame: ASSERT_INTERRUPTS_ENABLED mov %fs,%edi testb $2,UREGS_cs+8(%rsp) + ASM_STAC jz 1f /* Push new frame at registered guest-OS stack base. */ movl VCPU_kernel_sp(%rbx),%esi @@ -403,6 +404,7 @@ UNLIKELY_START(nz, compat_bounce_failsafe) movl %ds,%eax .Lft12: movl %eax,%fs:0*4(%rsi) # DS UNLIKELY_END(compat_bounce_failsafe) + ASM_CLAC /* Rewrite our stack frame and return to guest-OS mode. */ /* IA32 Ref. Vol. 3: TF, VM, RF and NT flags are cleared on trap. */ andl $~(X86_EFLAGS_VM|X86_EFLAGS_RF|\ @@ -448,6 +450,7 @@ compat_crash_page_fault_4: addl $4,%esi compat_crash_page_fault: .Lft14: mov %edi,%fs + ASM_CLAC movl %esi,%edi call show_page_walk jmp dom_crash_sync_extable diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index 6e27508..bdd1284 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -462,6 +462,7 @@ domain_crash_page_fault_16: domain_crash_page_fault_8: addq $8,%rsi domain_crash_page_fault: + ASM_CLAC movq %rsi,%rdi call show_page_walk ENTRY(dom_crash_sync_extable) -- 2.1.4