From c989ff614f6bad48b3bd4b32694f711b31c7b2d6 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 17 Feb 2025 15:51:51 +0000 Subject: [PATCH] x86/svm: Separate STI and VMRUN instructions in svm_asm_do_resume() There is a corner case in the VMRUN instruction where its INTR_SHADOW state leaks into guest state if a VMExit occurs before the VMRUN is complete. An example of this could be taking #NPF due to event injection. Xen can safely execute STI anywhere between CLGI and VMRUN, as CLGI blocks external interrupts too. However, an exception (while fatal) will appear to be in an irqs-on region (as GIF isn't considered), so position the STI after the speculation actions but prior to the GPR pops. Link: https://lore.kernel.org/all/CADH9ctBs1YPmE4aCfGPNBwA10cA8RuAk2gO7542DjMZgs4uzJQ@mail.gmail.com/ Fixes: 66b245d9eaeb ("SVM: limit GIF=0 region") Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich Release-Acked-by: Oleksii Kurochko --- xen/arch/x86/hvm/svm/entry.S | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/hvm/svm/entry.S b/xen/arch/x86/hvm/svm/entry.S index 6fd9652c04..91edb33459 100644 --- a/xen/arch/x86/hvm/svm/entry.S +++ b/xen/arch/x86/hvm/svm/entry.S @@ -74,6 +74,14 @@ __UNLIKELY_END(nsvm_hap) ALTERNATIVE "", svm_vmentry_spec_ctrl, X86_FEATURE_SC_MSR_HVM ALTERNATIVE "", DO_SPEC_CTRL_DIV, X86_FEATURE_SC_DIV + /* + * Set EFLAGS.IF after CLGI covers us from real interrupts, but not + * immediately prior to VMRUN. The VMRUN instruction leaks it's + * INTR_SHADOW into guest state if a VMExit occurs before VMRUN + * completes (e.g. taking #NPF during event injecting.) + */ + sti + pop %r15 pop %r14 pop %r13 @@ -91,7 +99,6 @@ __UNLIKELY_END(nsvm_hap) pop %rsi pop %rdi - sti vmrun SAVE_ALL