From 27d25348d42161837be08fc63b04a2559d2e781c Mon Sep 17 00:00:00 2001 From: Ashwin Dayanand Kamat Date: Wed, 29 Nov 2023 16:10:29 +0530 Subject: x86/sev: Fix kernel crash due to late update to read-only ghcb_version A write-access violation page fault kernel crash was observed while running cpuhotplug LTP testcases on SEV-ES enabled systems. The crash was observed during hotplug, after the CPU was offlined and the process was migrated to different CPU. setup_ghcb() is called again which tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this is a read_only variable which is initialised during booting. Trying to write it results in a pagefault: BUG: unable to handle page fault for address: ffffffffba556e70 #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation [ ...] Call Trace: ? __die_body.cold+0x1a/0x1f ? __die+0x2a/0x35 ? page_fault_oops+0x10c/0x270 ? setup_ghcb+0x71/0x100 ? __x86_return_thunk+0x5/0x6 ? search_exception_tables+0x60/0x70 ? __x86_return_thunk+0x5/0x6 ? fixup_exception+0x27/0x320 ? kernelmode_fixup_or_oops+0xa2/0x120 ? __bad_area_nosemaphore+0x16a/0x1b0 ? kernel_exc_vmm_communication+0x60/0xb0 ? bad_area_nosemaphore+0x16/0x20 ? do_kern_addr_fault+0x7a/0x90 ? exc_page_fault+0xbd/0x160 ? asm_exc_page_fault+0x27/0x30 ? setup_ghcb+0x71/0x100 ? setup_ghcb+0xe/0x100 cpu_init_exception_handling+0x1b9/0x1f0 The fix is to call sev_es_negotiate_protocol() only in the BSP boot phase, and it only needs to be done once in any case. [ mingo: Refined the changelog. ] Fixes: 95d33bfaa3e1 ("x86/sev: Register GHCB memory when SEV-SNP is active") Suggested-by: Tom Lendacky Co-developed-by: Bo Gan Signed-off-by: Bo Gan Signed-off-by: Ashwin Dayanand Kamat Signed-off-by: Ingo Molnar Acked-by: Tom Lendacky Link: https://lore.kernel.org/r/1701254429-18250-1-git-send-email-kashwindayan@vmware.com --- arch/x86/kernel/sev.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 70472eebe719..c67285824e82 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -1234,10 +1234,6 @@ void setup_ghcb(void) if (!cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) return; - /* First make sure the hypervisor talks a supported protocol. */ - if (!sev_es_negotiate_protocol()) - sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ); - /* * Check whether the runtime #VC exception handler is active. It uses * the per-CPU GHCB page which is set up by sev_es_init_vc_handling(). @@ -1254,6 +1250,13 @@ void setup_ghcb(void) return; } + /* + * Make sure the hypervisor talks a supported protocol. + * This gets called only in the BSP boot phase. + */ + if (!sev_es_negotiate_protocol()) + sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ); + /* * Clear the boot_ghcb. The first exception comes in before the bss * section is cleared. -- cgit v1.2.3 From 9b8493dc43044376716d789d07699f17d538a7c4 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Fri, 1 Dec 2023 19:37:27 +0100 Subject: x86/CPU/AMD: Check vendor in the AMD microcode callback Commit in Fixes added an AMD-specific microcode callback. However, it didn't check the CPU vendor the kernel runs on explicitly. The only reason the Zenbleed check in it didn't run on other x86 vendors hardware was pure coincidental luck: if (!cpu_has_amd_erratum(c, amd_zenbleed)) return; gives true on other vendors because they don't have those families and models. However, with the removal of the cpu_has_amd_erratum() in 05f5f73936fa ("x86/CPU/AMD: Drop now unused CPU erratum checking function") that coincidental condition is gone, leading to the zenbleed check getting executed on other vendors too. Add the explicit vendor check for the whole callback as it should've been done in the first place. Fixes: 522b1d69219d ("x86/cpu/amd: Add a Zenbleed fix") Cc: Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20231201184226.16749-1-bp@alien8.de --- arch/x86/kernel/cpu/amd.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index a7eab05e5f29..f322ebd053a9 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1320,6 +1320,9 @@ static void zenbleed_check_cpu(void *unused) void amd_check_microcode(void) { + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) + return; + on_each_cpu(zenbleed_check_cpu, NULL, 1); } -- cgit v1.2.3