5 files changed, 66 insertions, 8 deletions

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index fac1c4de7898..433b9554c6a1 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -121,6 +121,9 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/bug.h>
+#include <asm/processor.h> /* for signal_minsigstksz, used by ARCH_DLINFO */
+
 typedef unsigned long elf_greg_t;
 
 #define ELF_NGREG (sizeof(struct user_pt_regs) / sizeof(elf_greg_t))
@@ -148,6 +151,16 @@ typedef struct user_fpsimd_state elf_fpregset_t;
 do {                                                                    \
         NEW_AUX_ENT(AT_SYSINFO_EHDR,                                    \
                     (elf_addr_t)current->mm->context.vdso);             \
+                                                                        \
+        /*                                                              \
+         * Should always be nonzero unless there's a kernel bug.        \
+         * If we haven't determined a sensible value to give to         \
+         * userspace, omit the entry:                                   \
+         */                                                             \
+        if (likely(signal_minsigstksz))                                 \
+                NEW_AUX_ENT(AT_MINSIGSTKSZ, signal_minsigstksz);        \
+        else                                                            \
+                NEW_AUX_ENT(AT_IGNORE, 0);                              \
 } while (0)
 
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 767598932549..65ab83e8926e 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -35,6 +35,8 @@
 #ifdef __KERNEL__
 
 #include <linux/build_bug.h>
+#include <linux/cache.h>
+#include <linux/init.h>
 #include <linux/stddef.h>
 #include <linux/string.h>
 
@@ -244,6 +246,9 @@ void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused);
 void cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused);
 void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused);
 
+extern unsigned long __ro_after_init signal_minsigstksz; /* sigframe size */
+extern void __init minsigstksz_setup(void);
+
 /* Userspace interface for PR_SVE_{SET,GET}_VL prctl()s: */
 #define SVE_SET_VL(arg) sve_set_current_vl(arg)
 #define SVE_GET_VL()    sve_get_current_vl()
diff --git a/arch/arm64/include/uapi/asm/auxvec.h b/arch/arm64/include/uapi/asm/auxvec.h
index ec0a86d484e1..743c0b84fd30 100644
--- a/arch/arm64/include/uapi/asm/auxvec.h
+++ b/arch/arm64/include/uapi/asm/auxvec.h
@@ -19,7 +19,8 @@
 
 /* vDSO location */
 #define AT_SYSINFO_EHDR 33
+#define AT_MINSIGSTKSZ  51      /* stack needed for signal delivery */
 
-#define AT_VECTOR_SIZE_ARCH 1 /* entries in ARCH_DLINFO */
+#define AT_VECTOR_SIZE_ARCH 2 /* entries in ARCH_DLINFO */
 
 #endif
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index fbee8c17a4e6..d2856b129097 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1618,6 +1618,7 @@ void __init setup_cpu_features(void)
                 pr_info("emulated: Privileged Access Never (PAN) using TTBR0_EL1 switching\n");
 
         sve_setup();
+        minsigstksz_setup();
 
         /* Advertise that we have computed the system capabilities */
         set_sys_caps_initialised();
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 154b7d30145d..e7da5dba7ba8 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -17,6 +17,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <linux/cache.h>
 #include <linux/compat.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
@@ -570,8 +571,15 @@ badframe:
         return 0;
 }
 
-/* Determine the layout of optional records in the signal frame */
-static int setup_sigframe_layout(struct rt_sigframe_user_layout *user)
+/*
+ * Determine the layout of optional records in the signal frame
+ *
+ * add_all: if true, lays out the biggest possible signal frame for
+ *      this task; otherwise, generates a layout for the current state
+ *      of the task.
+ */
+static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
+                                 bool add_all)
 {
         int err;
 
@@ -581,7 +589,7 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user)
                 return err;
 
         /* fault information, if valid */
-        if (current->thread.fault_code) {
+        if (add_all || current->thread.fault_code) {
                 err = sigframe_alloc(user, &user->esr_offset,
                                      sizeof(struct esr_context));
                 if (err)
@@ -591,8 +599,14 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user)
         if (system_supports_sve()) {
                 unsigned int vq = 0;
 
-                if (test_thread_flag(TIF_SVE))
-                        vq = sve_vq_from_vl(current->thread.sve_vl);
+                if (add_all || test_thread_flag(TIF_SVE)) {
+                        int vl = sve_max_vl;
+
+                        if (!add_all)
+                                vl = current->thread.sve_vl;
+
+                        vq = sve_vq_from_vl(vl);
+                }
 
                 err = sigframe_alloc(user, &user->sve_offset,
                                      SVE_SIG_CONTEXT_SIZE(vq));
@@ -603,7 +617,6 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user)
         return sigframe_alloc_end(user);
 }
 
-
 static int setup_sigframe(struct rt_sigframe_user_layout *user,
                           struct pt_regs *regs, sigset_t *set)
 {
@@ -701,7 +714,7 @@ static int get_sigframe(struct rt_sigframe_user_layout *user,
         int err;
 
         init_user_layout(user);
-        err = setup_sigframe_layout(user);
+        err = setup_sigframe_layout(user, false);
         if (err)
                 return err;
 
@@ -936,3 +949,28 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
                 thread_flags = READ_ONCE(current_thread_info()->flags);
         } while (thread_flags & _TIF_WORK_MASK);
 }
+
+unsigned long __ro_after_init signal_minsigstksz;
+
+/*
+ * Determine the stack space required for guaranteed signal devliery.
+ * This function is used to populate AT_MINSIGSTKSZ at process startup.
+ * cpufeatures setup is assumed to be complete.
+ */
+void __init minsigstksz_setup(void)
+{
+        struct rt_sigframe_user_layout user;
+
+        init_user_layout(&user);
+
+        /*
+         * If this fails, SIGFRAME_MAXSZ needs to be enlarged.  It won't
+         * be big enough, but it's our best guess:
+         */
+        if (WARN_ON(setup_sigframe_layout(&user, true)))
+                return;
+
+        signal_minsigstksz = sigframe_size(&user) +
+                round_up(sizeof(struct frame_record), 16) +
+                16; /* max alignment padding */
+}