From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.cs.columbia.edu, linux-hardening@vger.kernel.org,
Ard Biesheuvel <ardb@kernel.org>, Will Deacon <will@kernel.org>,
Marc Zyngier <maz@kernel.org>, Fuad Tabba <tabba@google.com>,
Quentin Perret <qperret@google.com>,
Mark Rutland <mark.rutland@arm.com>,
James Morse <james.morse@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>
Subject: [RFC PATCH 04/12] arm64: mm: remap PGD pages r/o in the linear region after allocation
Date: Wed, 26 Jan 2022 18:30:03 +0100 [thread overview]
Message-ID: <20220126173011.3476262-5-ardb@kernel.org> (raw)
In-Reply-To: <20220126173011.3476262-1-ardb@kernel.org>
As the first step in restricting write access to all page tables via the
linear mapping, remap the page at the root PGD level of a user space
page table hierarchy read-only after allocation, so that it can only be
manipulated using the dedicated fixmap based API.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/mm/mmu.c | 7 ++++--
arch/arm64/mm/pgd.c | 25 ++++++++++++++------
2 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index acfae9b41cc8..a52c3162beae 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -394,8 +394,11 @@ static phys_addr_t __pgd_pgtable_alloc(int shift)
void *ptr = (void *)__get_free_page(GFP_PGTABLE_KERNEL);
BUG_ON(!ptr);
- /* Ensure the zeroed page is visible to the page table walker */
- dsb(ishst);
+ if (page_tables_are_ro())
+ set_pgtable_ro(ptr);
+ else
+ /* Ensure the zeroed page is visible to the page table walker */
+ dsb(ishst);
return __pa(ptr);
}
diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
index 4a64089e5771..637d6eceeada 100644
--- a/arch/arm64/mm/pgd.c
+++ b/arch/arm64/mm/pgd.c
@@ -9,8 +9,10 @@
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/highmem.h>
+#include <linux/set_memory.h>
#include <linux/slab.h>
+#include <asm/mmu_context.h>
#include <asm/pgalloc.h>
#include <asm/page.h>
#include <asm/tlbflush.h>
@@ -20,24 +22,33 @@ static struct kmem_cache *pgd_cache __ro_after_init;
pgd_t *pgd_alloc(struct mm_struct *mm)
{
gfp_t gfp = GFP_PGTABLE_USER;
+ pgd_t *pgd;
- if (PGD_SIZE == PAGE_SIZE)
- return (pgd_t *)__get_free_page(gfp);
- else
+ if (PGD_SIZE < PAGE_SIZE && !page_tables_are_ro())
return kmem_cache_alloc(pgd_cache, gfp);
+
+ pgd = (pgd_t *)__get_free_page(gfp);
+ if (!pgd)
+ return NULL;
+ if (page_tables_are_ro())
+ set_pgtable_ro(pgd);
+ return pgd;
}
void pgd_free(struct mm_struct *mm, pgd_t *pgd)
{
- if (PGD_SIZE == PAGE_SIZE)
- free_page((unsigned long)pgd);
- else
+ if (PGD_SIZE < PAGE_SIZE && !page_tables_are_ro()) {
kmem_cache_free(pgd_cache, pgd);
+ } else {
+ if (page_tables_are_ro())
+ set_pgtable_rw(pgd);
+ free_page((unsigned long)pgd);
+ }
}
void __init pgtable_cache_init(void)
{
- if (PGD_SIZE == PAGE_SIZE)
+ if (PGD_SIZE == PAGE_SIZE || page_tables_are_ro())
return;
#ifdef CONFIG_ARM64_PA_BITS_52
--
2.30.2
next prev parent reply other threads:[~2022-01-26 17:30 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 17:29 [RFC PATCH 00/12] arm64: implement read-only page tables Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 01/12] asm-generic/pgalloc: allow arch to override PMD alloc/free routines Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 02/12] arm64: mm: add helpers to remap page tables read-only/read-write Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 03/12] arm64: mm: use a fixmap slot for user page table modifications Ard Biesheuvel
2022-01-28 16:08 ` Steven Price
2022-01-26 17:30 ` Ard Biesheuvel [this message]
2022-01-26 17:30 ` [RFC PATCH 05/12] arm64: mm: remap PUD pages r/o in linear region Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 06/12] arm64: mm: remap PMD " Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 07/12] arm64: mm: remap PTE level user page tables r/o in the " Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 08/12] arm64: mm: remap kernel PTE level " Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 09/12] arm64: mm: remap kernel page tables read-only at end of init Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 10/12] mm: add default definition of p4d_index() Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 11/12] arm64: efi: use set_pte_at() not set_pte() in order to pass mm pointer Ard Biesheuvel
2022-01-26 17:30 ` [RFC PATCH 12/12] arm64: hugetlb: use set_pte_at() not set_pte() to provide " Ard Biesheuvel
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