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authorWill Deacon <will@kernel.org>2020-03-18 20:38:29 +0000
committerWill Deacon <will@kernel.org>2020-03-19 08:28:43 +0000
commitc83557859eaa1286330a4d3d2e1ea0c0988c4604 (patch)
tree71ae1a4d4b85e5f6d6494a62ce2b8e94dcb932dc
parentf50b7dacccbab2b9e3ef18f52a6dcc18ed2050b9 (diff)
arm64: kpti: Fix "kpti=off" when KASLR is enabled
Enabling KASLR forces the use of non-global page-table entries for kernel mappings, as this is a decision that we have to make very early on before mapping the kernel proper. When used in conjunction with the "kpti=off" command-line option, it is possible to use non-global kernel mappings but with the kpti trampoline disabled. Since commit 09e3c22a86f6 ("arm64: Use a variable to store non-global mappings decision"), arm64_kernel_unmapped_at_el0() reflects only the use of non-global mappings and does not take into account whether the kpti trampoline is enabled. This breaks context switching of the TPIDRRO_EL0 register for 64-bit tasks, where the clearing of the register is deferred to the ret-to-user code, but it also breaks the ARM SPE PMU driver which helpfully recommends passing "kpti=off" on the command line! Report whether or not KPTI is actually enabled in arm64_kernel_unmapped_at_el0() and check the 'arm64_use_ng_mappings' global variable directly when determining the protection flags for kernel mappings. Cc: Mark Brown <broonie@kernel.org> Reported-by: Hongbo Yao <yaohongbo@huawei.com> Tested-by: Hongbo Yao <yaohongbo@huawei.com> Fixes: 09e3c22a86f6 ("arm64: Use a variable to store non-global mappings decision") Signed-off-by: Will Deacon <will@kernel.org>
-rw-r--r--arch/arm64/include/asm/mmu.h4
-rw-r--r--arch/arm64/include/asm/pgtable-prot.h6
2 files changed, 5 insertions, 5 deletions
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index e4d862420bb4..d79ce6df9e12 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -29,11 +29,9 @@ typedef struct {
*/
#define ASID(mm) ((mm)->context.id.counter & 0xffff)
-extern bool arm64_use_ng_mappings;
-
static inline bool arm64_kernel_unmapped_at_el0(void)
{
- return arm64_use_ng_mappings;
+ return cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0);
}
typedef void (*bp_hardening_cb_t)(void);
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 6f87839f0249..1305e28225fc 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -23,11 +23,13 @@
#include <asm/pgtable-types.h>
+extern bool arm64_use_ng_mappings;
+
#define _PROT_DEFAULT (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
#define _PROT_SECT_DEFAULT (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
-#define PTE_MAYBE_NG (arm64_kernel_unmapped_at_el0() ? PTE_NG : 0)
-#define PMD_MAYBE_NG (arm64_kernel_unmapped_at_el0() ? PMD_SECT_NG : 0)
+#define PTE_MAYBE_NG (arm64_use_ng_mappings ? PTE_NG : 0)
+#define PMD_MAYBE_NG (arm64_use_ng_mappings ? PMD_SECT_NG : 0)
#define PROT_DEFAULT (_PROT_DEFAULT | PTE_MAYBE_NG)
#define PROT_SECT_DEFAULT (_PROT_SECT_DEFAULT | PMD_MAYBE_NG)