| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <ZshoLrEseHJZvyE_@google.com>
Date: Fri, 23 Aug 2024 10:45:02 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: akpm@...ux-foundation.org, alexghiti@...osinc.com, ankita@...dia.com,
ardb@...nel.org, catalin.marinas@....com,
christophe.leroy@...roup.eu, james.morse@....com,
vdonnefort@...gle.com, mark.rutland@....com, oliver.upton@...ux.dev,
rananta@...gle.com, ryan.roberts@....com, shahuang@...hat.com,
suzuki.poulose@....com, will@...nel.org, yuzenghui@...wei.com,
kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v8 4/6] KVM: arm64: Register ptdump with debugfs on guest
creation
On Tue, Aug 20, 2024 at 03:06:45PM +0100, Marc Zyngier wrote:
Hello Marc,
> On Fri, 16 Aug 2024 13:39:04 +0100,
> Sebastian Ene <sebastianene@...gle.com> wrote:
> >
> > While arch/*/mem/ptdump handles the kernel pagetable dumping code,
> > introduce KVM/ptdump which shows the guest stage-2 pagetables. The
> > separation is necessary because most of the definitions from the
> > stage-2 pagetable reside in the KVM path and we will be invoking
> > functionality **specific** to KVM.
>
> Drop the ** emphasis.
I will drop this.
>
> >
> > When a guest is created, register a new file entry under the guest
> > debugfs dir which allows userspace to show the contents of the guest
> > stage-2 pagetables when accessed.
> >
> > Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> > ---
> > arch/arm64/kvm/Kconfig | 14 ++++++
> > arch/arm64/kvm/Makefile | 1 +
> > arch/arm64/kvm/arm.c | 2 +
> > arch/arm64/kvm/kvm_ptdump.h | 20 ++++++++
> > arch/arm64/kvm/ptdump.c | 91 +++++++++++++++++++++++++++++++++++++
> > 5 files changed, 128 insertions(+)
> > create mode 100644 arch/arm64/kvm/kvm_ptdump.h
> > create mode 100644 arch/arm64/kvm/ptdump.c
> >
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > index 8304eb342be9..fcc41e58ede6 100644
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -66,4 +66,18 @@ config PROTECTED_NVHE_STACKTRACE
> >
> > If unsure, or not using protected nVHE (pKVM), say N.
> >
> > +config PTDUMP_STAGE2_DEBUGFS
> > + bool "Present the stage-2 pagetables to debugfs"
> > + depends on KVM
> > + select PTDUMP_CORE
>
> This looks wrong. Looking at PTDUMP_DEBUGFS, it has the following
> constraints:
>
> depends on DEBUG_KERNEL
> depends on DEBUG_FS
> depends on GENERIC_PTDUMP
> select PTDUMP_CORE
>
> I don't see why the Stage-2 version should have anything different.
>
> > + default n
> > + help
> > + Say Y here if you want to show the stage-2 kernel pagetables
> > + layout in a debugfs file. This information is only useful for kernel developers
> > + who are working in architecture specific areas of the kernel.
> > + It is probably not a good idea to enable this feature in a production
> > + kernel.
>
> nit: try to keep the formatting within 80 columns.
Let me fix the formatting and add the other depends on rules.
>
> More importantly, I find it very strange to expose the configuration
> option so early in the series, while the support code isn't there yet.
> You can perfectly introduce code that is conditional on a config
> option and only add it at the end.
I will move the configuration option as a separate patch in the last
part of the series.
>
> > +
> > + If in doubt, say N.
> > +
> > endif # VIRTUALIZATION
> > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> > index 86a629aaf0a1..e4233b323a73 100644
> > --- a/arch/arm64/kvm/Makefile
> > +++ b/arch/arm64/kvm/Makefile
> > @@ -27,6 +27,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
> >
> > kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o
> > kvm-$(CONFIG_ARM64_PTR_AUTH) += pauth.o
> > +kvm-$(CONFIG_PTDUMP_STAGE2_DEBUGFS) += ptdump.o
> >
> > always-y := hyp_constants.h hyp-constants.s
> >
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 9bef7638342e..60fed2146763 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -45,6 +45,7 @@
> > #include <kvm/arm_hypercalls.h>
> > #include <kvm/arm_pmu.h>
> > #include <kvm/arm_psci.h>
> > +#include <kvm_ptdump.h>
> >
> > static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
> >
> > @@ -228,6 +229,7 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> > void kvm_arch_create_vm_debugfs(struct kvm *kvm)
> > {
> > kvm_sys_regs_create_debugfs(kvm);
> > + kvm_ptdump_guest_register(kvm);
>
> Consider using a name that is homogeneous with what we already have
> (kvm_s2_ptdump_create_debugfs?).
>
> > }
> >
> > static void kvm_destroy_mpidr_data(struct kvm *kvm)
> > diff --git a/arch/arm64/kvm/kvm_ptdump.h b/arch/arm64/kvm/kvm_ptdump.h
> > new file mode 100644
> > index 000000000000..0a62b0e2908c
> > --- /dev/null
> > +++ b/arch/arm64/kvm/kvm_ptdump.h
> > @@ -0,0 +1,20 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (C) Google, 2024
> > + * Author: Sebastian Ene <sebastianene@...gle.com>
> > + */
> > +
> > +#ifndef __KVM_PTDUMP_H
> > +#define __KVM_PTDUMP_H
> > +
> > +#include <linux/kvm_host.h>
> > +#include <asm/ptdump.h>
> > +
> > +
> > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> > +void kvm_ptdump_guest_register(struct kvm *kvm);
> > +#else
> > +static inline void kvm_ptdump_guest_register(struct kvm *kvm) {}
> > +#endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
> > +
> > +#endif /* __KVM_PTDUMP_H */
>
> Please don't add new include files that contain so little stuff. These
> things may as well be added either to asm/kvm_host.h or asm/ptdump.h.
>
> > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> > new file mode 100644
> > index 000000000000..52483d56be2e
> > --- /dev/null
> > +++ b/arch/arm64/kvm/ptdump.c
> > @@ -0,0 +1,91 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Debug helper used to dump the stage-2 pagetables of the system and their
> > + * associated permissions.
> > + *
> > + * Copyright (C) Google, 2024
> > + * Author: Sebastian Ene <sebastianene@...gle.com>
> > + */
> > +#include <linux/debugfs.h>
> > +#include <linux/kvm_host.h>
> > +#include <linux/seq_file.h>
> > +
> > +#include <asm/kvm_pgtable.h>
> > +#include <kvm_ptdump.h>
> > +
> > +
> > +static int kvm_ptdump_visitor(const struct kvm_pgtable_visit_ctx *ctx,
> > + enum kvm_pgtable_walk_flags visit)
> > +{
> > + struct ptdump_pg_state *st = ctx->arg;
> > + struct ptdump_state *pt_st = &st->ptdump;
> > +
> > + note_page(pt_st, ctx->addr, ctx->level, ctx->old);
> > + return 0;
> > +}
> > +
> > +static int kvm_ptdump_show_common(struct seq_file *m,
>
> What does "common" mean here? You have exactly *one* caller, so why
> isn't that inlined in kvm_ptdump_guest_show()?
>
> > + struct kvm_pgtable *pgtable,
> > + struct ptdump_pg_state *parser_state)
> > +{
> > + struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
> > + .cb = kvm_ptdump_visitor,
> > + .arg = parser_state,
> > + .flags = KVM_PGTABLE_WALK_LEAF,
> > + };
> > +
> > + parser_state->level = -1;
> > + parser_state->start_address = 0;
> > +
> > + return kvm_pgtable_walk(pgtable, 0, BIT(pgtable->ia_bits), &walker);
> > +}
> > +
> > +static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
> > +{
> > + struct kvm *kvm = m->private;
> > + struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
> > + struct ptdump_pg_state parser_state = {0};
>
> nit: the common idiom is "parser_state = {}".
>
> > + int ret;
> > +
> > + write_lock(&kvm->mmu_lock);
> > + ret = kvm_ptdump_show_common(m, mmu->pgt, &parser_state);
> > + write_unlock(&kvm->mmu_lock);
> > +
> > + return ret;
> > +}
> > +
> > +static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
> > +{
> > + struct kvm *kvm = m->i_private;
> > + int ret;
> > +
> > + if (!kvm_get_kvm_safe(kvm))
> > + return -ENOENT;
> > +
> > + ret = single_open(file, kvm_ptdump_guest_show, m->i_private);
> > + if (ret < 0)
> > + kvm_put_kvm(kvm);
> > +
> > + return ret;
> > +}
> > +
> > +static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
> > +{
> > + struct kvm *kvm = m->i_private;
> > +
> > + kvm_put_kvm(kvm);
> > + return single_release(m, file);
> > +}
> > +
> > +static const struct file_operations kvm_ptdump_guest_fops = {
> > + .open = kvm_ptdump_guest_open,
> > + .read = seq_read,
> > + .llseek = seq_lseek,
> > + .release = kvm_ptdump_guest_close,
> > +};
> > +
> > +void kvm_ptdump_guest_register(struct kvm *kvm)
> > +{
> > + debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
> > + kvm, &kvm_ptdump_guest_fops);
> > +}
> > --
> > 2.46.0.184.g6999bdac58-goog
>
> Overall, I have a hard time understanding what this does. It walks the
> page tables, but doesn't do anything useful.
>
> I have the feeling that this patch would be better squashed together
> with patch #5, since it significantly reworks what patch #4 does.
>
Right, I think there are a few patches that should be squashed to
prevent this "empty" functionality.
Thanks for the feedback,
Seb
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
>
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@...roid.com.
>
Powered by blists - more mailing lists