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b=cPvzBruduJpLGbmc+gGMxSqlCZGgUaMYOmotAJNyAGv8lconA3N54WyhQvJYaKpAN wVlVdDJgtLaOv4mAqQnf7+FeDC/ig0Kdg3+yGfj2Hbh1L23LBMblmmdlQkmWruz8IS 1fTIRQs58pOwelCT2s9zGARgTZVnNE3Pm8+UErk0klGpDVBfNrxbC8RPxsbecx1zIu QHBG4rNFlOITsbRfgMu6XzWoOajmopGnocmA4baJH2oKjpPKPhZlfT7BtlBdsODQuv X8XbfS5V/8aV0l/vbtv5A7Ofh8MhISvZA/jlKUcnMypOMZrd135ADs/PA/q1/kCzCk ceO6mE5UiSMNA== Date: Mon, 20 Oct 2025 10:56:31 +0300 From: Mike Rapoport To: Pasha Tatashin Cc: akpm@linux-foundation.org, brauner@kernel.org, corbet@lwn.net, graf@amazon.com, jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, masahiroy@kernel.org, ojeda@kernel.org, pratyush@kernel.org, rdunlap@infradead.org, tj@kernel.org, jasonmiu@google.com, dmatlack@google.com, skhawaja@google.com Subject: Re: [PATCH v6 08/10] liveupdate: kho: warn and fail on metadata or preserved memory in scratch area Message-ID: References: <20251018171756.1724191-1-pasha.tatashin@soleen.com> <20251018171756.1724191-9-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251018171756.1724191-9-pasha.tatashin@soleen.com> X-Stat-Signature: k56sp9k1dc9kgmhajjfw5r1yco31a93b X-Rspamd-Queue-Id: 98479100004 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1760947001-328803 X-HE-Meta: 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 LSVkWkMT FqBGA6jMIuJGGxDqZV74j+fgVWVGoZE2GDjTTzYsCxd8OR2nut+S+oPmeZVV3y+t2atXim3efLuA2ACYzxLj7W3K1pcZ+SqapEvpChfW+xffl9l0VUTOzVMq1G4rD1UYLzrYINmrBV8z26uBTGDkaJYLVMrH9uwWUxjbHxX9HPZ4wdn/rOXtfKfS1wsT17H87o/qMHwuB6la/BJTrjRWW+R8ZWPxEzPt4ktayU7uoLuW6YNA893e1jLr5uadtJCyRO+gG9aBweGkv6cRPmOFxTXQvc7s/ncHUTWc0etRXFj12G4uAF5Vscn5KnKz32KgY6zgwFGKx3v7aIUUmmRtGa4px30d+78JVWLEVhwtV+xnlJP2KohjaT3E65o/WkCDRv4q8 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Oct 18, 2025 at 01:17:54PM -0400, Pasha Tatashin wrote: > It is invalid for KHO metadata or preserved memory regions to be located > within the KHO scratch area, as this area is overwritten when the next > kernel is loaded, and used early in boot by the next kernel. This can > lead to memory corruption. > > Adds checks to kho_preserve_* and KHO's internal metadata allocators > (xa_load_or_alloc, new_chunk) to verify that the physical address of the > memory does not overlap with any defined scratch region. If an overlap > is detected, the operation will fail and a WARN_ON is triggered. To > avoid performance overhead in production kernels, these checks are > enabled only when CONFIG_KEXEC_HANDOVER_DEBUG is selected. > > Signed-off-by: Pasha Tatashin > --- > kernel/liveupdate/Kconfig | 8 ++++ > kernel/liveupdate/Makefile | 1 + > kernel/liveupdate/kexec_handover.c | 52 ++++++++++++++------- > kernel/liveupdate/kexec_handover_debug.c | 25 ++++++++++ > kernel/liveupdate/kexec_handover_internal.h | 9 ++++ > 5 files changed, 78 insertions(+), 17 deletions(-) > create mode 100644 kernel/liveupdate/kexec_handover_debug.c > > diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig > index cea287842475..851d1a22b4c5 100644 > --- a/kernel/liveupdate/Kconfig > +++ b/kernel/liveupdate/Kconfig > @@ -27,4 +27,12 @@ config KEXEC_HANDOVER_DEBUGFS > Also, enables inspecting the KHO fdt trees with the debugfs binary > blobs. > > +config KEXEC_HANDOVER_DEBUG > + bool "Enable Kexec Handover debug checks" > + depends on KEXEC_HANDOVER_DEBUGFS > + help > + This option enables extra sanity checks for the Kexec Handover > + subsystem. Since, KHO performance is crucial in live update > + scenarios and the extra code might be adding overhead it is > + only optionally enabled. And empty line here would be nice. > endmenu > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index c87d00c40c82..ebfc31814d16 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -8,6 +8,7 @@ > > #define pr_fmt(fmt) "KHO: " fmt > > +#include > #include > #include > #include > @@ -131,26 +132,26 @@ static struct kho_out kho_out = { > > static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t sz) > { > - void *elm, *res; > + void *res = xa_load(xa, index); > > - elm = xa_load(xa, index); > - if (elm) > - return elm; > + if (res) > + return res; > + > + void *elm __free(kfree) = kzalloc(sz, GFP_KERNEL); > > - elm = kzalloc(sz, GFP_KERNEL); > if (!elm) > return ERR_PTR(-ENOMEM); > > + if (WARN_ON(kho_scratch_overlap(virt_to_phys(elm), sz))) I'd move the WARN_ON into kho_scratch_overlap(). > + return ERR_PTR(-EINVAL); > + > res = xa_cmpxchg(xa, index, NULL, elm, GFP_KERNEL); > if (xa_is_err(res)) > - res = ERR_PTR(xa_err(res)); > - > - if (res) { > - kfree(elm); > + return ERR_PTR(xa_err(res)); > + else if (res) > return res; > - } > > - return elm; > + return no_free_ptr(elm); > } ... > @@ -379,14 +384,17 @@ static int kho_mem_serialize(struct kho_out *kho_out) > struct khoser_mem_chunk *chunk = NULL; > struct kho_mem_phys *physxa; > unsigned long order; > + int ret = -ENOMEM; Nit: s/ret/err/ > > xa_for_each(&kho_out->track.orders, order, physxa) { > struct kho_mem_phys_bits *bits; > unsigned long phys; > > diff --git a/kernel/liveupdate/kexec_handover_debug.c b/kernel/liveupdate/kexec_handover_debug.c > new file mode 100644 > index 000000000000..7986dcc63047 > --- /dev/null > +++ b/kernel/liveupdate/kexec_handover_debug.c > @@ -0,0 +1,25 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * kexec_handover_debug.c - kexec handover optional debug functionality > + * Copyright (C) 2025 Google LLC, Pasha Tatashin > + */ > + > +#define pr_fmt(fmt) "KHO: " fmt > + > +#include "kexec_handover_internal.h" > + > +bool kho_scratch_overlap(phys_addr_t phys, size_t size) > +{ > + phys_addr_t scratch_start, scratch_end; > + unsigned int i; > + > + for (i = 0; i < kho_scratch_cnt; i++) { > + scratch_start = kho_scratch[i].addr; > + scratch_end = kho_scratch[i].addr + kho_scratch[i].size - 1; I agree with Pratyush that scratch_end = kho_scratch[i].addr + kho_scratch[i].size; if (phys < scratch_end ... is clearer. > + if (phys <= scratch_end && (phys + size) > scratch_start) > + return true; > + } > + > + return false; > +} -- Sincerely yours, Mike.