From 78004e9a87f240df03e2f73120d291763c32e0a7 Mon Sep 17 00:00:00 2001 From: Ali Ahmet Memis Date: Fri, 21 Aug 2026 01:45:27 +0000 Subject: openrisc: fix arbitrary kernel memory access via or1k_atomic syscall sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user pointers, v1 and v2, and swaps the words they point to in hand-written assembly. l.lwz r29,0(r4) l.lwz r27,0(r5) l.sw 0(r4),r27 l.sw 0(r5),r29 The pointers are not checked with access_ok(). The four memory accesses also have no exception table entries. A caller passes a kernel address as either pointer, and the syscall reads from and writes to it directly. This gives an unprivileged process a kernel read/write primitive. It overwrites kernel data such as the sys_call_table, gaining code execution in kernel context. Check both pointers before entering the critical section. Add fixups for the four memory accesses so faults on valid but unmapped user addresses return -EFAULT. [shorne@gmail.com: fix comment style] Fixes: 9d02a4283e9c ("OpenRISC: Boot code") Cc: stable@vger.kernel.org Signed-off-by: Ali Ahmet Memis Signed-off-by: Stafford Horne --- arch/x86/entry/common.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 arch/x86/entry/common.c (limited to 'arch/x86/entry/common.c') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c new file mode 100644 index 000000000..14cd43d4d --- /dev/null +++ b/arch/x86/entry/common.c @@ -0,0 +1,61 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include +#include +#include +#include + +#if IS_ENABLED(CONFIG_KVM_INTEL) +/* + * On VMX, NMIs and IRQs (as configured by KVM) are acknowledged by hardware as + * part of the VM-Exit, i.e. the event itself is consumed as part the VM-Exit. + * x86_entry_from_kvm() is invoked by KVM to effectively forward NMIs and IRQs + * to the kernel for servicing. On SVM, a.k.a. AMD, the NMI/IRQ VM-Exit is + * purely a signal that an NMI/IRQ is pending, i.e. the event that triggered + * the VM-Exit is held pending until it's unblocked in the host. + */ +noinstr void x86_entry_from_kvm(unsigned int event_type, unsigned int vector) +{ + if (event_type == EVENT_TYPE_EXTINT) { +#ifdef CONFIG_X86_64 + /* + * Use FRED dispatch, even when running IDT. The dispatch + * tables are kept in sync between FRED and IDT, and the FRED + * dispatch works well with CFI. + */ + fred_entry_from_kvm(event_type, vector); +#else + idt_entry_from_kvm(vector); +#endif + /* + * Strictly speaking, only the NMI path requires noinstr. + */ + instrumentation_begin(); + /* + * KVM/VMX will dispatch from IRQ-disabled but for a context + * that will have IRQs-enabled. This confuses the entry code + * and it will not have reprogrammed the timer. Do so now. + */ + hrtimer_rearm_deferred(); + instrumentation_end(); + + return; + } + + WARN_ON_ONCE(event_type != EVENT_TYPE_NMI); + +#ifdef CONFIG_X86_64 + if (cpu_feature_enabled(X86_FEATURE_FRED)) + return fred_entry_from_kvm(event_type, vector); +#endif + + /* + * Notably, we must use IDT dispatch for NMI when running in IDT mode. + * The FRED NMI context is significantly different and will not work + * right (specifically FRED fixed the NMI recursion issue). + */ + idt_do_nmi_irqoff(); +} +EXPORT_SYMBOL_FOR_KVM(x86_entry_from_kvm); +#endif -- cgit v1.3.1