From 6c43c72748fffd29dec15cd1f31e9a32949bc437 Mon Sep 17 00:00:00 2001 From: Melody Wang Date: Mon, 14 Sep 2026 00:57:17 +0000 Subject: x86/sev: Make vTPM SVSM calls preemption-safe Two functions in the SVSM vTPM guest implementation do not disable preemption when fetching the SVSM Calling Area Address (CAA). The SVSM CAA is a per-CPU structure. When a thread is preempted and migrated to a different CPU after fetching the per-CPU CAA, the SVSM call will execute on the new CPU with the original CPU's CAA. Which is wrong. Move the CAA fetching operation inside svsm_perform_call_protocol() which disables interrupts around the SVSM call and thus runs preemption-safe. Fixes: 770de678bc28 ("x86/sev: Add SVSM vTPM probe/send_command functions") Signed-off-by: Melody Wang Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Stefano Garzarella Cc: stable@vger.kernel.org Link: https://patch.msgid.link/a5bc0d4a2c462a0089109e145c21626b244b2ff0.1789345277.git.huibo.wang@amd.com --- arch/x86/coco/sev/svsm.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/coco/sev/svsm.c b/arch/x86/coco/sev/svsm.c index 916d62cd1..2d493d55f 100644 --- a/arch/x86/coco/sev/svsm.c +++ b/arch/x86/coco/sev/svsm.c @@ -74,6 +74,14 @@ int svsm_perform_call_protocol(struct svsm_call *call) flags = native_local_irq_save(); + /* + * 'caa' is a per-CPU variable. To avoid using a stale or incorrect + * 'caa' if the task is preempted or migrated to another CPU after it + * is fetched, always fetch 'caa' and then issue the SVSM call with + * interrupts disabled. This ensures the correct 'caa' is used. + */ + call->caa = svsm_get_caa(); + ghcb = __sev_get_ghcb(&state); do { @@ -321,7 +329,6 @@ int snp_svsm_vtpm_send_command(u8 *buffer) { struct svsm_call call = {}; - call.caa = svsm_get_caa(); call.rax = SVSM_VTPM_CALL(SVSM_VTPM_CMD); call.rcx = __pa(buffer); @@ -345,7 +352,6 @@ bool snp_svsm_vtpm_probe(void) if (!snp_vmpl) return false; - call.caa = svsm_get_caa(); call.rax = SVSM_VTPM_CALL(SVSM_VTPM_QUERY); if (svsm_perform_call_protocol(&call)) -- cgit v1.3.1