From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 7ba36eccb3f83983a651efd570b4f933ecad1b5c ]
The arm64 ptdump code can race with concurrent modification of the kernel page tables. At the time this was added, this was sound as:
* Modifications to leaf entries could result in stale information being logged, but would not result in a functional problem.
* Boot time modifications to non-leaf entries (e.g. freeing of initmem) were performed when the ptdump code cannot be invoked.
* At runtime, modifications to non-leaf entries only occurred in the vmalloc region, and these were strictly additive, as intermediate entries were never freed.
However, since commit:
commit 324420bf91f6 ("arm64: add support for ioremap() block mappings")
... it has been possible to create huge mappings in the vmalloc area at runtime, and as part of this existing intermediate levels of table my be removed and freed.
It's possible for the ptdump code to race with this, and continue to walk tables which have been freed (and potentially poisoned or reallocated). As a result of this, the ptdump code may dereference bogus addresses, which could be fatal.
Since huge-vmap is a TLB and memory optimization, we can disable it when the runtime ptdump code is in use to avoid this problem.
Cc: Catalin Marinas catalin.marinas@arm.com Fixes: 324420bf91f60582 ("arm64: add support for ioremap() block mappings") Acked-by: Ard Biesheuvel ard.biesheuvel@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Anshuman Khandual anshuman.khandual@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/mm/mmu.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 6ac0d32d60a5..abb9d2ecc675 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -899,13 +899,18 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
int __init arch_ioremap_pud_supported(void) { - /* only 4k granule supports level 1 block mappings */ - return IS_ENABLED(CONFIG_ARM64_4K_PAGES); + /* + * Only 4k granule supports level 1 block mappings. + * SW table walks can't handle removal of intermediate entries. + */ + return IS_ENABLED(CONFIG_ARM64_4K_PAGES) && + !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); }
int __init arch_ioremap_pmd_supported(void) { - return 1; + /* See arch_ioremap_pud_supported() */ + return !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); }
int pud_set_huge(pud_t *pud, phys_addr_t phys, pgprot_t prot)