[PATCH v8 4/4] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

Based on aarch64 implementation, provide a 32 bit entry point for
this vDSO.

In order to keep compatibility with arm64_futex_robust_unlock_get_pop(),
make sure to store the pop address at r2 and the compare result value
at r3.

Signed-off-by: André Almeida <[email protected]>
---
v7:
 - The store needs to be a release store, so s/strex/stlex/
 - result reg clobber modified to "=&r" to make sure the compiler don't use
 the r3 reg for something else
 - pop_reg will be read after the execution so it should be an output
 parameter with "+Q"
---
 arch/arm64/kernel/vdso.c            | 15 ++++++++++++++-
 arch/arm64/kernel/vdso32/Makefile   |  4 ++++
 arch/arm64/kernel/vdso32/vdso.lds.S |  9 +++++++++
 arch/arm64/kernel/vdso32/vfutex.c   | 34 ++++++++++++++++++++++++++++++++++
 4 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index dc6b582736d0..5cae9c17ec72 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -78,11 +78,19 @@ static inline void vdso_futex_update_ips(struct mm_struct *mm)
 				VDSO_SYMBOL(vdso, futex_list64_try_unlock_cs_end));
 }
 
+static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm)
+{
+	unsigned long vdso = (unsigned long) mm->context.vdso;
+
+	__vdso_futex_update_ips(mm, true,
+				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_start),
+				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_end));
+}
 #else
 static inline void vdso_futex_update_ips(struct mm_struct *mm) {}
+static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm) {}
 #endif /* CONFIG_FUTEX_ROBUST_UNLOCK */
 
-
 static int vdso_mremap(const struct vm_special_mapping *sm,
 		struct vm_area_struct *new_vma)
 {
@@ -195,6 +203,8 @@ static int aarch32_mremap(const struct vm_special_mapping *sm,
 {
 	current->mm->context.vdso = (void *)new_vma->vm_start;
 
+	aarch32_vdso_futex_update_ips(current->mm);
+
 	return 0;
 }
 
@@ -327,6 +337,7 @@ static int aarch32_sigreturn_setup(struct mm_struct *mm)
 	return PTR_ERR_OR_ZERO(ret);
 }
 
+
 int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	struct mm_struct *mm = current->mm;
@@ -347,6 +358,8 @@ int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	}
 
 	ret = aarch32_sigreturn_setup(mm);
+
+	aarch32_vdso_futex_update_ips(mm);
 out:
 	mmap_write_unlock(mm);
 	return ret;
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 4bd60f059f4a..f3190125c68b 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -97,6 +97,10 @@ munge := ../../../arm/vdso/vdsomunge
 hostprogs := $(munge)
 
 c-obj-vdso := note.o
+ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+  c-obj-vdso += vfutex.o
+endif
+
 c-obj-vdso-gettimeofday := vgettimeofday.o
 
 ifneq ($(c-gettimeofday-y),)
diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
index 12bfc39e8aab..52ced27d6045 100644
--- a/arch/arm64/kernel/vdso32/vdso.lds.S
+++ b/arch/arm64/kernel/vdso32/vdso.lds.S
@@ -89,6 +89,15 @@ VERSION
 #endif /* CONFIG_COMPAT_32BIT_TIME */
 		__vdso_clock_gettime64;
 		__vdso_clock_getres_time64;
+#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+		__vdso_futex_robust_list32_try_unlock;
+#endif
 	local: *;
 	};
 }
+
+#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+VDSO_futex_list32_try_unlock_cs_success = __futex_list32_try_unlock_cs_success;
+VDSO_futex_list32_try_unlock_cs_start = __futex_list32_try_unlock_cs_start;
+VDSO_futex_list32_try_unlock_cs_end = __futex_list32_try_unlock_cs_end;
+#endif
diff --git a/arch/arm64/kernel/vdso32/vfutex.c b/arch/arm64/kernel/vdso32/vfutex.c
new file mode 100644
index 000000000000..0d9080b17965
--- /dev/null
+++ b/arch/arm64/kernel/vdso32/vfutex.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/stringify.h>
+#include <vdso/futex.h>
+
+__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop)
+{
+	register __u32 *pop_reg asm("r2") = pop, result_reg asm("r3") = 0;
+	__u32 val, zero = 0;
+
+	asm volatile (
+		".globl						  "
+		"__futex_list32_try_unlock_cs_start,		  "
+		"__futex_list32_try_unlock_cs_success,		  "
+		"__futex_list32_try_unlock_cs_end		\n"
+
+		"retry:						\n"
+		"	ldrex %[val], %[lock]			\n"
+		"	cmp %[tid], %[val]			\n"
+		"	bne __futex_list32_try_unlock_cs_end	\n"
+		"	stlex %[result], %[zero], %[lock]	\n"
+		"__futex_list32_try_unlock_cs_start:		\n"
+		"	cmp %[result], #0			\n"
+		"	bne retry				\n"
+		"__futex_list32_try_unlock_cs_success:		\n"
+		"	str %[zero], %[pop_reg]			\n"
+		"__futex_list32_try_unlock_cs_end:		\n"
+
+		: [val] "=&r" (val), [result] "=&r" (result_reg), [pop_reg] "+Q" (*pop_reg)
+		: [tid] "r" (tid), [lock] "Q" (*lock), [zero] "r" (zero)
+		: "cc", "memory"
+	);
+
+	return val;
+}

-- 
2.55.0