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charset="utf-8" X-RootMTR: 20260609062228eucas1p211850bcf6ea79ef270bc6fbe29ffafdb X-EPHeader: CA X-CMS-RootMailID: 20260609062228eucas1p211850bcf6ea79ef270bc6fbe29ffafdb References: <20260529150150.1670604-17-ardb+git@google.com> <20260529150150.1670604-32-ardb+git@google.com> Dear All, On 29.05.2026 17:02, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > The linear aliases of the kernel text and rodata are also mapped > read-only in the linear map. Given that the contents of these regions > are mostly identical to the version in the loadable image, mapping them > read-only and leaving their contents visible is a reasonable hardening > measure. > > Data and bss, however, are now also mapped read-only but the contents of > these regions are more likely to contain data that we'd rather not leak. > So let's unmap these entirely in the linear map when the kernel is > running normally. > > When going into hibernation or waking up from it, these regions need to > be mapped, so map the region initially, and toggle the valid bit so > map/unmap the region as needed. > > Doing so is required because pages covering the kernel image are marked > as PageReserved, and therefore disregarded for snapshotting by the > hibernate logic unless they are mapped. > > Signed-off-by: Ard Biesheuvel This commit landed in yesterday's linux-next as commit 63e0b6a5b693 ("arm64: mm: Unmap kernel data/bss entirely from the linear map"). In my tests I found that it breaks booting of RaspberryPi3 and RaspberryPi4 boards with the following kernel panic: kvm [1]: nv: 570 coarse grained trap handlers kvm [1]: nv: 710 fine grained trap handlers kvm [1]: IPA Size Limit: 40 bits Unable to handle kernel paging request at virtual address ffff000003a23000 Mem abort info:   ESR = 0x0000000096000147   EC = 0x25: DABT (current EL), IL = 32 bits   SET = 0, FnV = 0   EA = 0, S1PTW = 0   FSC = 0x07: level 3 translation fault Data abort info:   ISV = 0, ISS = 0x00000147, ISS2 = 0x00000000   CM = 1, WnR = 1, TnD = 0, TagAccess = 0   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000002609000 [ffff000003a23000] pgd=0000000000000000, p4d=180000003b3ff403, pud=180000003b3fe403, pmd=180000003b3e6403, pte=00e8000003a23f06 Internal error: Oops: 0000000096000147 [#1]  SMP Modules linked in: CPU: 3 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.1.0-rc1+ #16768 PREEMPT Hardware name: Raspberry Pi 3 Model B (DT) pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : dcache_clean_inval_poc+0x24/0x48 lr : kvm_arm_init+0xa8c/0x165c sp : ffff8000844bbd00 ... Call trace:  dcache_clean_inval_poc+0x24/0x48 (P)  do_one_initcall+0x68/0x4f4  kernel_init_freeable+0x24c/0x360  kernel_init+0x24/0x1dc  ret_from_fork+0x10/0x20 Code: 9ac32042 d1000443 8a230000 d503201f (d50b7e20) ---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b SMP: stopping secondary CPUs Kernel Offset: disabled CPU features: 0x00000000,03000008,00040000,0400421b Memory Limit: none ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]--- > --- > arch/arm64/mm/mmu.c | 45 ++++++++++++++++++-- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 7b18dc2f1721..07a6fa210171 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -24,6 +24,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1056,6 +1057,29 @@ static void __init __map_memblock(phys_addr_t start, phys_addr_t end, > end - start, prot, early_pgtable_alloc, flags); > } > > +static void mark_linear_data_alias_valid(bool valid) > +{ > + set_memory_valid((unsigned long)lm_alias(__init_end), > + (unsigned long)(__bss_stop - __init_end) / PAGE_SIZE, > + valid); > +} > + > +static int arm64_hibernate_pm_notify(struct notifier_block *nb, > + unsigned long mode, void *unused) > +{ > + switch (mode) { > + default: > + break; > + case PM_POST_HIBERNATION: > + mark_linear_data_alias_valid(false); > + break; > + case PM_HIBERNATION_PREPARE: > + mark_linear_data_alias_valid(true); > + break; > + } > + return 0; > +} > + > void __init mark_linear_text_alias_ro(void) > { > /* > @@ -1064,6 +1088,21 @@ void __init mark_linear_text_alias_ro(void) > update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text), > (unsigned long)__init_begin - (unsigned long)_text, > PAGE_KERNEL_RO); > + > + /* > + * Register a PM notifier to remap the linear alias of data/bss as > + * valid read-only before hibernation. This is needed because the > + * snapshot logic disregards PageReserved pages (such as the ones > + * covering the kernel image) unless they are mapped in the linear > + * map. > + */ > + if (IS_ENABLED(CONFIG_HIBERNATION)) { > + static struct notifier_block nb = { > + .notifier_call = arm64_hibernate_pm_notify > + }; > + > + register_pm_notifier(&nb); > + } > } > > #ifdef CONFIG_KFENCE > @@ -1193,10 +1232,8 @@ static void __init map_mem(void) > flags); > } > > - /* Map the kernel data/bss read-only in the linear map */ > - __map_memblock(init_end, kernel_end, PAGE_KERNEL_RO, flags); > - flush_tlb_kernel_range((unsigned long)lm_alias(__init_end), > - (unsigned long)lm_alias(__bss_stop)); > + /* Map the kernel data/bss as invalid in the linear map */ > + mark_linear_data_alias_valid(false); > } > > void mark_rodata_ro(void) Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland