[PATCH v4 05/12] arm64: remove the ability to build a kernel without kpti

From: Jeremy Linton
Date: Fri Jan 25 2019 - 13:08:01 EST

Buried behind EXPERT is the ability to build a kernel without
hardened branch predictors, this needlessly clutters up the
code as well as creates the opportunity for bugs. It also
removes the kernel's ability to determine if the machine its
running on is vulnerable.

Since its also possible to disable it at boot time, lets remove
the config option.

Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
---
arch/arm64/Kconfig | 12 ------------
arch/arm64/include/asm/fixmap.h | 2 --
arch/arm64/include/asm/mmu.h | 7 +------
arch/arm64/include/asm/sdei.h | 2 +-
arch/arm64/kernel/asm-offsets.c | 2 --
arch/arm64/kernel/cpufeature.c | 4 ----
arch/arm64/kernel/entry.S | 11 +----------
arch/arm64/kernel/sdei.c | 2 --
arch/arm64/kernel/vmlinux.lds.S | 8 --------
arch/arm64/mm/context.c | 6 ------
arch/arm64/mm/mmu.c | 2 --
arch/arm64/mm/proc.S | 2 --
12 files changed, 3 insertions(+), 57 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6b4c6d3fdf4d..09a85410d814 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -993,18 +993,6 @@ config FORCE_MAX_ZONEORDER
However for 4K, we choose a higher default value, 11 as opposed to 10, giving us
4M allocations matching the default size used by generic code.

-config UNMAP_KERNEL_AT_EL0
- bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT
- default y
- help
- Speculation attacks against some high-performance processors can
- be used to bypass MMU permission checks and leak kernel data to
- userspace. This can be defended against by unmapping the kernel
- when running in userspace, mapping it back in on exception entry
- via a trampoline page in the vector table.
-
- If unsure, say Y.
-
config HARDEN_EL2_VECTORS
bool "Harden EL2 vector mapping against system register leak" if EXPERT
default y
diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index ec1e6d6fa14c..62371f07d4ce 100644
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -58,11 +58,9 @@ enum fixed_addresses {
FIX_APEI_GHES_NMI,
#endif /* CONFIG_ACPI_APEI_GHES */

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
FIX_ENTRY_TRAMP_DATA,
FIX_ENTRY_TRAMP_TEXT,
#define TRAMP_VALIAS (__fix_to_virt(FIX_ENTRY_TRAMP_TEXT))
-#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
__end_of_permanent_fixed_addresses,

/*
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 20fdf71f96c3..9d689661471c 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -42,18 +42,13 @@ typedef struct {

static inline bool arm64_kernel_unmapped_at_el0(void)
{
- return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) &&
- cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0);
+ return cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0);
}

static inline bool arm64_kernel_use_ng_mappings(void)
{
bool tx1_bug;

- /* What's a kpti? Use global mappings if we don't know. */
- if (!IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0))
- return false;
-
/*
* Note: this function is called before the CPU capabilities have
* been configured, so our early mappings will be global. If we
diff --git a/arch/arm64/include/asm/sdei.h b/arch/arm64/include/asm/sdei.h
index ffe47d766c25..82c3e9b6a4b0 100644
--- a/arch/arm64/include/asm/sdei.h
+++ b/arch/arm64/include/asm/sdei.h
@@ -23,7 +23,7 @@ extern unsigned long sdei_exit_mode;
asmlinkage void __sdei_asm_handler(unsigned long event_num, unsigned long arg,
unsigned long pc, unsigned long pstate);

-/* and its CONFIG_UNMAP_KERNEL_AT_EL0 trampoline */
+/* and its unmap kernel at el0 trampoline */
asmlinkage void __sdei_asm_entry_trampoline(unsigned long event_num,
unsigned long arg,
unsigned long pc,
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 65b8afc84466..6a6f83de91b8 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -165,9 +165,7 @@ int main(void)
DEFINE(HIBERN_PBE_NEXT, offsetof(struct pbe, next));
DEFINE(ARM64_FTR_SYSVAL, offsetof(struct arm64_ftr_reg, sys_val));
BLANK();
-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
DEFINE(TRAMP_VALIAS, TRAMP_VALIAS);
-#endif
#ifdef CONFIG_ARM_SDE_INTERFACE
DEFINE(SDEI_EVENT_INTREGS, offsetof(struct sdei_registered_event, interrupted_regs));
DEFINE(SDEI_EVENT_PRIORITY, offsetof(struct sdei_registered_event, priority));
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index d1a7fd7972f9..a9e18b9cdc1e 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -944,7 +944,6 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
return has_cpuid_feature(entry, scope);
}

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */

static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
@@ -1035,7 +1034,6 @@ static int __init parse_kpti(char *str)
return 0;
}
early_param("kpti", parse_kpti);
-#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */

#ifdef CONFIG_ARM64_HW_AFDBM
static inline void __cpu_enable_hw_dbm(void)
@@ -1284,7 +1282,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.field_pos = ID_AA64PFR0_EL0_SHIFT,
.min_field_value = ID_AA64PFR0_EL0_32BIT_64BIT,
},
-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
{
.desc = "Kernel page table isolation (KPTI)",
.capability = ARM64_UNMAP_KERNEL_AT_EL0,
@@ -1300,7 +1297,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.matches = unmap_kernel_at_el0,
.cpu_enable = kpti_install_ng_mappings,
},
-#endif
{
/* FP/SIMD is not implemented */
.capability = ARM64_HAS_NO_FPSIMD,
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 3f0eaaf704c8..1d8efc144b04 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -70,7 +70,6 @@

.macro kernel_ventry, el, label, regsize = 64
.align 7
-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
alternative_if ARM64_UNMAP_KERNEL_AT_EL0
.if \el == 0
.if \regsize == 64
@@ -81,7 +80,6 @@ alternative_if ARM64_UNMAP_KERNEL_AT_EL0
.endif
.endif
alternative_else_nop_endif
-#endif

sub sp, sp, #S_FRAME_SIZE
#ifdef CONFIG_VMAP_STACK
@@ -345,7 +343,6 @@ alternative_else_nop_endif

.if \el == 0
alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
bne 4f
msr far_el1, x30
tramp_alias x30, tramp_exit_native
@@ -353,7 +350,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
4:
tramp_alias x30, tramp_exit_compat
br x30
-#endif
+
.else
eret
.endif
@@ -913,7 +910,6 @@ ENDPROC(el0_svc)

.popsection // .entry.text

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
/*
* Exception vectors trampoline.
*/
@@ -1023,7 +1019,6 @@ __entry_tramp_data_start:
.quad vectors
.popsection // .rodata
#endif /* CONFIG_RANDOMIZE_BASE */
-#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */

/*
* Register switch for AArch64. The callee-saved registers need to be saved
@@ -1086,7 +1081,6 @@ NOKPROBE(ret_from_fork)
b .
.endm

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
/*
* The regular SDEI entry point may have been unmapped along with the rest of
* the kernel. This trampoline restores the kernel mapping to make the x1 memory
@@ -1146,7 +1140,6 @@ __sdei_asm_trampoline_next_handler:
.quad __sdei_asm_handler
.popsection // .rodata
#endif /* CONFIG_RANDOMIZE_BASE */
-#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */

/*
* Software Delegated Exception entry point.
@@ -1240,10 +1233,8 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
sdei_handler_exit exit_mode=x2
alternative_else_nop_endif

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
tramp_alias dst=x5, sym=__sdei_asm_exit_trampoline
br x5
-#endif
ENDPROC(__sdei_asm_handler)
NOKPROBE(__sdei_asm_handler)
#endif /* CONFIG_ARM_SDE_INTERFACE */
diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c
index 5ba4465e44f0..a0dbdb962019 100644
--- a/arch/arm64/kernel/sdei.c
+++ b/arch/arm64/kernel/sdei.c
@@ -157,7 +157,6 @@ unsigned long sdei_arch_get_entry_point(int conduit)

sdei_exit_mode = (conduit == CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
if (arm64_kernel_unmapped_at_el0()) {
unsigned long offset;

@@ -165,7 +164,6 @@ unsigned long sdei_arch_get_entry_point(int conduit)
(unsigned long)__entry_tramp_text_start;
return TRAMP_VALIAS + offset;
} else
-#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
return (unsigned long)__sdei_asm_handler;

}
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 7fa008374907..a4dbee11bcb5 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -57,16 +57,12 @@ jiffies = jiffies_64;
#define HIBERNATE_TEXT
#endif

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
#define TRAMP_TEXT \
. = ALIGN(PAGE_SIZE); \
__entry_tramp_text_start = .; \
*(.entry.tramp.text) \
. = ALIGN(PAGE_SIZE); \
__entry_tramp_text_end = .;
-#else
-#define TRAMP_TEXT
-#endif

/*
* The size of the PE/COFF section that covers the kernel image, which
@@ -143,10 +139,8 @@ SECTIONS
idmap_pg_dir = .;
. += IDMAP_DIR_SIZE;

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
tramp_pg_dir = .;
. += PAGE_SIZE;
-#endif

#ifdef CONFIG_ARM64_SW_TTBR0_PAN
reserved_ttbr0 = .;
@@ -257,10 +251,8 @@ ASSERT(__idmap_text_end - (__idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
ASSERT(__hibernate_exit_text_end - (__hibernate_exit_text_start & ~(SZ_4K - 1))
<= SZ_4K, "Hibernate exit text too big or misaligned")
#endif
-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == PAGE_SIZE,
"Entry trampoline text too big")
-#endif
/*
* If padding is applied before .head.text, virt<->phys conversions will fail.
*/
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 1f0ea2facf24..e99f3e645e06 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -40,15 +40,9 @@ static cpumask_t tlb_flush_pending;
#define ASID_MASK (~GENMASK(asid_bits - 1, 0))
#define ASID_FIRST_VERSION (1UL << asid_bits)

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
#define NUM_USER_ASIDS (ASID_FIRST_VERSION >> 1)
#define asid2idx(asid) (((asid) & ~ASID_MASK) >> 1)
#define idx2asid(idx) (((idx) << 1) & ~ASID_MASK)
-#else
-#define NUM_USER_ASIDS (ASID_FIRST_VERSION)
-#define asid2idx(asid) ((asid) & ~ASID_MASK)
-#define idx2asid(idx) asid2idx(idx)
-#endif

/* Get the ASIDBits supported by the current CPU */
static u32 get_cpu_asid_bits(void)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b6f5aa52ac67..97252baf4700 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -570,7 +570,6 @@ static int __init parse_rodata(char *arg)
}
early_param("rodata", parse_rodata);

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
static int __init map_entry_trampoline(void)
{
pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;
@@ -597,7 +596,6 @@ static int __init map_entry_trampoline(void)
return 0;
}
core_initcall(map_entry_trampoline);
-#endif

/*
* Create fine-grained mappings for the kernel.
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 73886a5f1f30..e9ca5cbb93bc 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -217,7 +217,6 @@ ENTRY(idmap_cpu_replace_ttbr1)
ENDPROC(idmap_cpu_replace_ttbr1)
.popsection

-#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
.pushsection ".idmap.text", "awx"

.macro __idmap_kpti_get_pgtable_ent, type
@@ -406,7 +405,6 @@ __idmap_kpti_secondary:
.unreq pte
ENDPROC(idmap_kpti_install_ng_mappings)
.popsection
-#endif

/*
* __cpu_setup
--
2.17.2