[PATCH 24/35] arm64: mte: Switch GCR_EL1 in kernel entry and exit
Andrey Konovalov
andreyknvl at google.com
Fri Aug 14 13:27:06 EDT 2020
From: Vincenzo Frascino <vincenzo.frascino at arm.com>
When MTE is present, the GCR_EL1 register contains the tags mask that
allows to exclude tags from the random generation via the IRG instruction.
With the introduction of the new Tag-Based KASAN API that provides a
mechanism to reserve tags for special reasons, the MTE implementation
has to make sure that the GCR_EL1 setting for the kernel does not affect
the userspace processes and viceversa.
Save and restore the kernel/user mask in GCR_EL1 in kernel entry and exit.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
---
arch/arm64/include/asm/mte.h | 8 ++++++++
arch/arm64/kernel/asm-offsets.c | 3 +++
arch/arm64/kernel/cpufeature.c | 5 +++--
arch/arm64/kernel/entry.S | 28 ++++++++++++++++++++++++++++
arch/arm64/kernel/mte.c | 19 +++++++++++++++++--
5 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 733be1cb5c95..4929f744d103 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -21,6 +21,8 @@
#include <asm/pgtable-types.h>
+extern u64 gcr_kernel_excl;
+
void mte_clear_page_tags(void *addr);
unsigned long mte_copy_tags_from_user(void *to, const void __user *from,
unsigned long n);
@@ -59,6 +61,8 @@ u8 mte_get_mem_tag(void *addr);
u8 mte_get_random_tag(void);
void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
+void mte_init_tags(u64 max_tag);
+
#else /* CONFIG_ARM64_MTE */
/* unused if !CONFIG_ARM64_MTE, silence the compiler */
@@ -120,6 +124,10 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
return addr;
}
+static inline void mte_init_tags(u64 max_tag)
+{
+}
+
#endif /* CONFIG_ARM64_MTE */
#endif /* __ASSEMBLY__ */
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 0577e2142284..a1ef256cad4f 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -47,6 +47,9 @@ int main(void)
#ifdef CONFIG_ARM64_PTR_AUTH
DEFINE(THREAD_KEYS_USER, offsetof(struct task_struct, thread.keys_user));
DEFINE(THREAD_KEYS_KERNEL, offsetof(struct task_struct, thread.keys_kernel));
+#endif
+#ifdef CONFIG_ARM64_MTE
+ DEFINE(THREAD_GCR_EL1_USER, offsetof(struct task_struct, thread.gcr_user_excl));
#endif
BLANK();
DEFINE(S_X0, offsetof(struct pt_regs, regs[0]));
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4d94af19d8f6..54bc3b315063 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1665,14 +1665,15 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
{
u64 mair;
- /* all non-zero tags excluded by default */
- write_sysreg_s(SYS_GCR_EL1_RRND | SYS_GCR_EL1_EXCL_MASK, SYS_GCR_EL1);
write_sysreg_s(0, SYS_TFSR_EL1);
write_sysreg_s(0, SYS_TFSRE0_EL1);
/* Enable Match-All at EL1 */
sysreg_clear_set(tcr_el1, 0, SYS_TCR_EL1_TCMA1);
+ /* Enable the kernel exclude mask for random tags generation */
+ write_sysreg_s((SYS_GCR_EL1_RRND | gcr_kernel_excl), SYS_GCR_EL1);
+
/*
* CnP must be enabled only after the MAIR_EL1 register has been set
* up. Inconsistent MAIR_EL1 between CPUs sharing the same TLB may
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index cde127508e38..a17fefb0571b 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -172,6 +172,29 @@ alternative_else_nop_endif
#endif
.endm
+ /* Note: tmp should always be a callee-saved register */
+ .macro mte_restore_gcr, el, tsk, tmp, tmp2
+#ifdef CONFIG_ARM64_MTE
+alternative_if_not ARM64_MTE
+ b 1f
+alternative_else_nop_endif
+ .if \el == 0
+ ldr \tmp, [\tsk, #THREAD_GCR_EL1_USER]
+ .else
+ ldr_l \tmp, gcr_kernel_excl
+ .endif
+ /*
+ * Calculate and set the exclude mask preserving
+ * the RRND (bit[16]) setting.
+ */
+ mrs_s \tmp2, SYS_GCR_EL1
+ bfi \tmp2, \tmp, #0, #16
+ msr_s SYS_GCR_EL1, \tmp2
+ isb
+1:
+#endif
+ .endm
+
.macro kernel_entry, el, regsize = 64
.if \regsize == 32
mov w0, w0 // zero upper 32 bits of x0
@@ -209,6 +232,8 @@ alternative_else_nop_endif
ptrauth_keys_install_kernel tsk, x20, x22, x23
+ mte_restore_gcr 1, tsk, x22, x23
+
scs_load tsk, x20
.else
add x21, sp, #S_FRAME_SIZE
@@ -386,6 +411,8 @@ alternative_else_nop_endif
/* No kernel C function calls after this as user keys are set. */
ptrauth_keys_install_user tsk, x0, x1, x2
+ mte_restore_gcr 0, tsk, x0, x1
+
apply_ssbd 0, x0, x1
.endif
@@ -957,6 +984,7 @@ SYM_FUNC_START(cpu_switch_to)
mov sp, x9
msr sp_el0, x1
ptrauth_keys_install_kernel x1, x8, x9, x10
+ mte_restore_gcr 1, x1, x8, x9
scs_save x0, x8
scs_load x1, x8
ret
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 7717ea9bc2a7..cfac7d02f032 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -18,10 +18,14 @@
#include <asm/barrier.h>
#include <asm/cpufeature.h>
+#include <asm/kasan.h>
+#include <asm/kprobes.h>
#include <asm/mte.h>
#include <asm/ptrace.h>
#include <asm/sysreg.h>
+u64 gcr_kernel_excl __read_mostly;
+
static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
{
pte_t old_pte = READ_ONCE(*ptep);
@@ -115,6 +119,13 @@ void * __must_check mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
return ptr;
}
+void mte_init_tags(u64 max_tag)
+{
+ u64 incl = ((1ULL << ((max_tag & MTE_TAG_MAX) + 1)) - 1);
+
+ gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
+}
+
static void update_sctlr_el1_tcf0(u64 tcf0)
{
/* ISB required for the kernel uaccess routines */
@@ -150,7 +161,11 @@ static void update_gcr_el1_excl(u64 excl)
static void set_gcr_el1_excl(u64 excl)
{
current->thread.gcr_user_excl = excl;
- update_gcr_el1_excl(excl);
+
+ /*
+ * SYS_GCR_EL1 will be set to current->thread.gcr_user_incl value
+ * by mte_restore_gcr() in kernel_exit,
+ */
}
void flush_mte_state(void)
@@ -184,7 +199,7 @@ void mte_suspend_exit(void)
if (!system_supports_mte())
return;
- update_gcr_el1_excl(current->thread.gcr_user_excl);
+ update_gcr_el1_excl(gcr_kernel_excl);
}
long set_mte_ctrl(struct task_struct *task, unsigned long arg)
--
2.28.0.220.ged08abb693-goog
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