1 files changed, 223 insertions, 12 deletions

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index c7d311d8b92a..14ac6fdb872b 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -26,6 +26,7 @@
 #include <asm/elf.h>
 #include <asm/exception.h>
 #include <asm/cacheflush.h>
+#include <asm/gcs.h>
 #include <asm/ucontext.h>
 #include <asm/unistd.h>
 #include <asm/fpsimd.h>
@@ -35,6 +36,15 @@
 #include <asm/traps.h>
 #include <asm/vdso.h>
 
+#ifdef CONFIG_ARM64_GCS
+#define GCS_SIGNAL_CAP(addr) (((unsigned long)addr) & GCS_CAP_ADDR_MASK)
+
+static bool gcs_signal_cap_valid(u64 addr, u64 val)
+{
+	return val == GCS_SIGNAL_CAP(addr);
+}
+#endif
+
 /*
  * Do a signal return; undo the signal stack. These are aligned to 128-bit.
  */
@@ -43,11 +53,6 @@ struct rt_sigframe {
 	struct ucontext uc;
 };
 
-struct frame_record {
-	u64 fp;
-	u64 lr;
-};
-
 struct rt_sigframe_user_layout {
 	struct rt_sigframe __user *sigframe;
 	struct frame_record __user *next_frame;
@@ -57,6 +62,7 @@ struct rt_sigframe_user_layout {
 
 	unsigned long fpsimd_offset;
 	unsigned long esr_offset;
+	unsigned long gcs_offset;
 	unsigned long sve_offset;
 	unsigned long tpidr2_offset;
 	unsigned long za_offset;
@@ -79,7 +85,6 @@ struct user_access_state {
 	u64 por_el0;
 };
 
-#define BASE_SIGFRAME_SIZE round_up(sizeof(struct rt_sigframe), 16)
 #define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16)
 #define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16)
 
@@ -242,6 +247,8 @@ struct user_ctxs {
 	u32 fpmr_size;
 	struct poe_context __user *poe;
 	u32 poe_size;
+	struct gcs_context __user *gcs;
+	u32 gcs_size;
 };
 
 static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
@@ -689,6 +696,82 @@ extern int restore_zt_context(struct user_ctxs *user);
 
 #endif /* ! CONFIG_ARM64_SME */
 
+#ifdef CONFIG_ARM64_GCS
+
+static int preserve_gcs_context(struct gcs_context __user *ctx)
+{
+	int err = 0;
+	u64 gcspr = read_sysreg_s(SYS_GCSPR_EL0);
+
+	/*
+	 * If GCS is enabled we will add a cap token to the frame,
+	 * include it in the GCSPR_EL0 we report to support stack
+	 * switching via sigreturn if GCS is enabled.  We do not allow
+	 * enabling via sigreturn so the token is only relevant for
+	 * threads with GCS enabled.
+	 */
+	if (task_gcs_el0_enabled(current))
+		gcspr -= 8;
+
+	__put_user_error(GCS_MAGIC, &ctx->head.magic, err);
+	__put_user_error(sizeof(*ctx), &ctx->head.size, err);
+	__put_user_error(gcspr, &ctx->gcspr, err);
+	__put_user_error(0, &ctx->reserved, err);
+	__put_user_error(current->thread.gcs_el0_mode,
+			 &ctx->features_enabled, err);
+
+	return err;
+}
+
+static int restore_gcs_context(struct user_ctxs *user)
+{
+	u64 gcspr, enabled;
+	int err = 0;
+
+	if (user->gcs_size != sizeof(*user->gcs))
+		return -EINVAL;
+
+	__get_user_error(gcspr, &user->gcs->gcspr, err);
+	__get_user_error(enabled, &user->gcs->features_enabled, err);
+	if (err)
+		return err;
+
+	/* Don't allow unknown modes */
+	if (enabled & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
+		return -EINVAL;
+
+	err = gcs_check_locked(current, enabled);
+	if (err != 0)
+		return err;
+
+	/* Don't allow enabling */
+	if (!task_gcs_el0_enabled(current) &&
+	    (enabled & PR_SHADOW_STACK_ENABLE))
+		return -EINVAL;
+
+	/* If we are disabling disable everything */
+	if (!(enabled & PR_SHADOW_STACK_ENABLE))
+		enabled = 0;
+
+	current->thread.gcs_el0_mode = enabled;
+
+	/*
+	 * We let userspace set GCSPR_EL0 to anything here, we will
+	 * validate later in gcs_restore_signal().
+	 */
+	write_sysreg_s(gcspr, SYS_GCSPR_EL0);
+
+	return 0;
+}
+
+#else /* ! CONFIG_ARM64_GCS */
+
+/* Turn any non-optimised out attempts to use these into a link error: */
+extern int preserve_gcs_context(void __user *ctx);
+extern int restore_gcs_context(struct user_ctxs *user);
+
+#endif /* ! CONFIG_ARM64_GCS */
+
 static int parse_user_sigframe(struct user_ctxs *user,
 			       struct rt_sigframe __user *sf)
 {
@@ -707,6 +790,7 @@ static int parse_user_sigframe(struct user_ctxs *user,
 	user->zt = NULL;
 	user->fpmr = NULL;
 	user->poe = NULL;
+	user->gcs = NULL;
 
 	if (!IS_ALIGNED((unsigned long)base, 16))
 		goto invalid;
@@ -823,6 +907,17 @@ static int parse_user_sigframe(struct user_ctxs *user,
 			user->fpmr_size = size;
 			break;
 
+		case GCS_MAGIC:
+			if (!system_supports_gcs())
+				goto invalid;
+
+			if (user->gcs)
+				goto invalid;
+
+			user->gcs = (struct gcs_context __user *)head;
+			user->gcs_size = size;
+			break;
+
 		case EXTRA_MAGIC:
 			if (have_extra_context)
 				goto invalid;
@@ -943,6 +1038,9 @@ static int restore_sigframe(struct pt_regs *regs,
 			err = restore_fpsimd_context(&user);
 	}
 
+	if (err == 0 && system_supports_gcs() && user.gcs)
+		err = restore_gcs_context(&user);
+
 	if (err == 0 && system_supports_tpidr2() && user.tpidr2)
 		err = restore_tpidr2_context(&user);
 
@@ -961,6 +1059,58 @@ static int restore_sigframe(struct pt_regs *regs,
 	return err;
 }
 
+#ifdef CONFIG_ARM64_GCS
+static int gcs_restore_signal(void)
+{
+	unsigned long __user *gcspr_el0;
+	u64 cap;
+	int ret;
+
+	if (!system_supports_gcs())
+		return 0;
+
+	if (!(current->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE))
+		return 0;
+
+	gcspr_el0 = (unsigned long __user *)read_sysreg_s(SYS_GCSPR_EL0);
+
+	/*
+	 * Ensure that any changes to the GCS done via GCS operations
+	 * are visible to the normal reads we do to validate the
+	 * token.
+	 */
+	gcsb_dsync();
+
+	/*
+	 * GCSPR_EL0 should be pointing at a capped GCS, read the cap.
+	 * We don't enforce that this is in a GCS page, if it is not
+	 * then faults will be generated on GCS operations - the main
+	 * concern is to protect GCS pages.
+	 */
+	ret = copy_from_user(&cap, gcspr_el0, sizeof(cap));
+	if (ret)
+		return -EFAULT;
+
+	/*
+	 * Check that the cap is the actual GCS before replacing it.
+	 */
+	if (!gcs_signal_cap_valid((u64)gcspr_el0, cap))
+		return -EINVAL;
+
+	/* Invalidate the token to prevent reuse */
+	put_user_gcs(0, (__user void*)gcspr_el0, &ret);
+	if (ret != 0)
+		return -EFAULT;
+
+	write_sysreg_s(gcspr_el0 + 1, SYS_GCSPR_EL0);
+
+	return 0;
+}
+
+#else
+static int gcs_restore_signal(void) { return 0; }
+#endif
+
 SYSCALL_DEFINE0(rt_sigreturn)
 {
 	struct pt_regs *regs = current_pt_regs();
@@ -985,6 +1135,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	if (restore_sigframe(regs, frame, &ua_state))
 		goto badframe;
 
+	if (gcs_restore_signal())
+		goto badframe;
+
 	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
@@ -1024,6 +1177,15 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
 			return err;
 	}
 
+#ifdef CONFIG_ARM64_GCS
+	if (system_supports_gcs() && (add_all || current->thread.gcspr_el0)) {
+		err = sigframe_alloc(user, &user->gcs_offset,
+				     sizeof(struct gcs_context));
+		if (err)
+			return err;
+	}
+#endif
+
 	if (system_supports_sve() || system_supports_sme()) {
 		unsigned int vq = 0;
 
@@ -1132,6 +1294,12 @@ static int setup_sigframe(struct rt_sigframe_user_layout *user,
 		__put_user_error(current->thread.fault_code, &esr_ctx->esr, err);
 	}
 
+	if (system_supports_gcs() && err == 0 && user->gcs_offset) {
+		struct gcs_context __user *gcs_ctx =
+			apply_user_offset(user, user->gcs_offset);
+		err |= preserve_gcs_context(gcs_ctx);
+	}
+
 	/* Scalable Vector Extension state (including streaming), if present */
 	if ((system_supports_sve() || system_supports_sme()) &&
 	    err == 0 && user->sve_offset) {
@@ -1154,7 +1322,7 @@ static int setup_sigframe(struct rt_sigframe_user_layout *user,
 		err |= preserve_fpmr_context(fpmr_ctx);
 	}
 
-	if (system_supports_poe() && err == 0 && user->poe_offset) {
+	if (system_supports_poe() && err == 0) {
 		struct poe_context __user *poe_ctx =
 			apply_user_offset(user, user->poe_offset);
 
@@ -1249,7 +1417,48 @@ static int get_sigframe(struct rt_sigframe_user_layout *user,
 	return 0;
 }
 
-static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
+#ifdef CONFIG_ARM64_GCS
+
+static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig)
+{
+	unsigned long __user *gcspr_el0;
+	int ret = 0;
+
+	if (!system_supports_gcs())
+		return 0;
+
+	if (!task_gcs_el0_enabled(current))
+		return 0;
+
+	/*
+	 * We are entering a signal handler, current register state is
+	 * active.
+	 */
+	gcspr_el0 = (unsigned long __user *)read_sysreg_s(SYS_GCSPR_EL0);
+
+	/*
+	 * Push a cap and the GCS entry for the trampoline onto the GCS.
+	 */
+	put_user_gcs((unsigned long)sigtramp, gcspr_el0 - 2, &ret);
+	put_user_gcs(GCS_SIGNAL_CAP(gcspr_el0 - 1), gcspr_el0 - 1, &ret);
+	if (ret != 0)
+		return ret;
+
+	gcspr_el0 -= 2;
+	write_sysreg_s((unsigned long)gcspr_el0, SYS_GCSPR_EL0);
+
+	return 0;
+}
+#else
+
+static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig)
+{
+	return 0;
+}
+
+#endif
+
+static int setup_return(struct pt_regs *regs, struct ksignal *ksig,
 			 struct rt_sigframe_user_layout *user, int usig)
 {
 	__sigrestore_t sigtramp;
@@ -1257,7 +1466,7 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
 	regs->regs[0] = usig;
 	regs->sp = (unsigned long)user->sigframe;
 	regs->regs[29] = (unsigned long)&user->next_frame->fp;
-	regs->pc = (unsigned long)ka->sa.sa_handler;
+	regs->pc = (unsigned long)ksig->ka.sa.sa_handler;
 
 	/*
 	 * Signal delivery is a (wacky) indirect function call in
@@ -1297,12 +1506,14 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
 		sme_smstop();
 	}
 
-	if (ka->sa.sa_flags & SA_RESTORER)
-		sigtramp = ka->sa.sa_restorer;
+	if (ksig->ka.sa.sa_flags & SA_RESTORER)
+		sigtramp = ksig->ka.sa.sa_restorer;
 	else
 		sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
 
 	regs->regs[30] = (unsigned long)sigtramp;
+
+	return gcs_signal_entry(sigtramp, ksig);
 }
 
 static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
@@ -1327,7 +1538,7 @@ static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
 	err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
 	err |= setup_sigframe(&user, regs, set, &ua_state);
 	if (err == 0) {
-		setup_return(regs, &ksig->ka, &user, usig);
+		err = setup_return(regs, ksig, &user, usig);
 		if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
 			err |= copy_siginfo_to_user(&frame->info, &ksig->info);
 			regs->regs[1] = (unsigned long)&frame->info;