[PATCH v2] arm64: errata: Fix exec handling in erratum 1418040 workaround

[D Scott Phillips]

The erratum 1418040 workaround changes vct access trapping when switching
between compat and non-compat threads. The workaround logic assumes that
the hardware vct trapping state matches the previous task's compat-ness.
However, when a non-compat task execs a compat binary or vice versa, the
cntkctl state and task compat-ness get out of sync. Keep the hardware
trapping state in sync with the task personality.

Fixes: d49f7d7376d0 ("arm64: Move handling of erratum 1418040 into C code")
Signed-off-by: D Scott Phillips <scott at os.amperecomputing.com>
Reviewed-by: Marc Zyngier <maz at kernel.org>
Cc: <stable at vger.kernel.org> # 5.4.x
---

 v2: - Use sysreg_clear_set instead of open coding (Marc)
     - guard this_cpu_has_cap() check under IS_ENABLED() to avoid tons of
       WARN_ON(preemptible()) when built with !CONFIG_ARM64_ERRATUM_1418040

 arch/arm64/include/asm/elf.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 97932fbf973d..24036b914226 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -160,8 +160,16 @@ typedef struct user_fpsimd_state elf_fpregset_t;
 
 #define SET_PERSONALITY(ex)						\
 ({									\
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040))			\
+		preempt_disable();					\
 	clear_thread_flag(TIF_32BIT);					\
 	current->personality &= ~READ_IMPLIES_EXEC;			\
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) {			\
+		if (this_cpu_has_cap(ARM64_WORKAROUND_1418040))		\
+			sysreg_clear_set(cntkctl_el1, 0,		\
+					 ARCH_TIMER_USR_VCT_ACCESS_EN);	\
+		preempt_enable();					\
+	}								\
 })
 
 /* update AT_VECTOR_SIZE_ARCH if the number of NEW_AUX_ENT entries changes */
@@ -223,7 +231,16 @@ int compat_elf_check_arch(const struct elf32_hdr *);
  */
 #define COMPAT_SET_PERSONALITY(ex)					\
 ({									\
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040))			\
+		preempt_disable();					\
 	set_thread_flag(TIF_32BIT);					\
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) {			\
+		if (this_cpu_has_cap(ARM64_WORKAROUND_1418040))		\
+			sysreg_clear_set(cntkctl_el1,			\
+					 ARCH_TIMER_USR_VCT_ACCESS_EN,	\
+					 0);				\
+		preempt_enable();					\
+	}								\
  })
 #ifdef CONFIG_COMPAT_VDSO
 #define COMPAT_ARCH_DLINFO						\
-- 
2.31.1