riscv: signal: abstract header saving for setup_sigcontext

The function save_v_state() served two purposes. First, it saved
extension context into the signal stack. Then, it constructed the
extension header if there was no fault. The second part is independent
of the extension itself. As a result, we can pull that part out, so
future extensions may reuse it. This patch adds arch_ext_list and makes
setup_sigcontext() go through all possible extensions' save() callback.
The callback returns a positive value indicating the size of the
successfully saved extension. Then the kernel proceeds to construct the
header for that extension. The kernel skips an extension if it does
not exist, or if the saving fails for some reasons. The error code is
propagated out on the later case.

This patch does not introduce any functional changes.

Signed-off-by: Andy Chiu <andybnac@gmail.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-16-b55691eacf4f@rivosinc.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: AndybnACT

arch/riscv/include/asm/vector.h

@@ -424,6 +424,9 @@ static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
 #define riscv_v_thread_free(tsk)		do {} while (0)
 #define  riscv_v_setup_ctx_cache()		do {} while (0)
 #define riscv_v_thread_alloc(tsk)		do {} while (0)
+#define get_cpu_vector_context()		do {} while (0)
+#define put_cpu_vector_context()		do {} while (0)
+#define riscv_v_vstate_set_restore(task, regs)	do {} while (0)
 
 #endif /* CONFIG_RISCV_ISA_V */
 

arch/riscv/kernel/signal.c

@@ -68,18 +68,19 @@ static long save_fp_state(struct pt_regs *regs,
 #define restore_fp_state(task, regs) (0)
 #endif
 
-#ifdef CONFIG_RISCV_ISA_V
-
-static long save_v_state(struct pt_regs *regs, void __user **sc_vec)
+static long save_v_state(struct pt_regs *regs, void __user *sc_vec)
 {
-	struct __riscv_ctx_hdr __user *hdr;
 	struct __sc_riscv_v_state __user *state;
 	void __user *datap;
 	long err;
 
-	hdr = *sc_vec;
-	/* Place state to the user's signal context space after the hdr */
-	state = (struct __sc_riscv_v_state __user *)(hdr + 1);
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_V) ||
+	    !((has_vector() || has_xtheadvector()) &&
+	    riscv_v_vstate_query(regs)))
+		return 0;
+
+	/* Place state to the user's signal context space */
+	state = (struct __sc_riscv_v_state __user *)sc_vec;
 	/* Point datap right after the end of __sc_riscv_v_state */
 	datap = state + 1;
 
@@ -97,15 +98,11 @@ static long save_v_state(struct pt_regs *regs, void __user **sc_vec)
 	err |= __put_user((__force void *)datap, &state->v_state.datap);
 	/* Copy the whole vector content to user space datap. */
 	err |= __copy_to_user(datap, current->thread.vstate.datap, riscv_v_vsize);
-	/* Copy magic to the user space after saving  all vector conetext */
-	err |= __put_user(RISCV_V_MAGIC, &hdr->magic);
-	err |= __put_user(riscv_v_sc_size, &hdr->size);
 	if (unlikely(err))
-		return err;
+		return -EFAULT;
 
-	/* Only progress the sv_vec if everything has done successfully  */
-	*sc_vec += riscv_v_sc_size;
-	return 0;
+	/* Only return the size if everything has done successfully  */
+	return riscv_v_sc_size;
 }
 
 /*
@@ -142,10 +139,20 @@ static long __restore_v_state(struct pt_regs *regs, void __user *sc_vec)
 	 */
 	return copy_from_user(current->thread.vstate.datap, datap, riscv_v_vsize);
 }
-#else
-#define save_v_state(task, regs) (0)
-#define __restore_v_state(task, regs) (0)
-#endif
+
+struct arch_ext_priv {
+	__u32 magic;
+	long (*save)(struct pt_regs *regs, void __user *sc_vec);
+};
+
+struct arch_ext_priv arch_ext_list[] = {
+	{
+		.magic = RISCV_V_MAGIC,
+		.save = &save_v_state,
+	},
+};
+
+const size_t nr_arch_exts = ARRAY_SIZE(arch_ext_list);
 
 static long restore_sigcontext(struct pt_regs *regs,
 	struct sigcontext __user *sc)
@@ -270,16 +277,29 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
 {
 	struct sigcontext __user *sc = &frame->uc.uc_mcontext;
 	struct __riscv_ctx_hdr __user *sc_ext_ptr = &sc->sc_extdesc.hdr;
-	long err;
+	struct arch_ext_priv *arch_ext;
+	long err, i, ext_size;
 
 	/* sc_regs is structured the same as the start of pt_regs */
 	err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
 	/* Save the floating-point state. */
 	if (has_fpu())
 		err |= save_fp_state(regs, &sc->sc_fpregs);
 	/* Save the vector state. */
-	if ((has_vector() || has_xtheadvector()) && riscv_v_vstate_query(regs))
-		err |= save_v_state(regs, (void __user **)&sc_ext_ptr);
+	for (i = 0; i < nr_arch_exts; i++) {
+		arch_ext = &arch_ext_list[i];
+		if (!arch_ext->save)
+			continue;
+
+		ext_size = arch_ext->save(regs, sc_ext_ptr + 1);
+		if (ext_size <= 0) {
+			err |= ext_size;
+		} else {
+			err |= __put_user(arch_ext->magic, &sc_ext_ptr->magic);
+			err |= __put_user(ext_size, &sc_ext_ptr->size);
+			sc_ext_ptr = (void *)sc_ext_ptr + ext_size;
+		}
+	}
 	/* Write zero to fp-reserved space and check it on restore_sigcontext */
 	err |= __put_user(0, &sc->sc_extdesc.reserved);
 	/* And put END __riscv_ctx_hdr at the end. */