lib: sbi: call platform load/store emulators

sbi_load/store_access_handler now tries to call platform emulators
if defined. Otherwise, redirects the fault. If the platform code
returns failure, this means the H/S/U has accessed the emulated
devices in an unexpected manner, which is very likely caused by
buggy code in H/S/U. We redirect the fault, so lower privileged
level can get notified, and act accordingly. (E.g., oops in Linux)

We let the handler truly fail if the trap was originated from M mode.
In this case, something must be very wrong and we should just fail.

Signed-off-by: Bo Gan <ganboing@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

2 files changed, 80 insertions, 2 deletions

diff --git a/include/sbi/sbi_platform.h b/include/sbi/sbi_platform.h
index f962aa4..581935a 100644
--- a/include/sbi/sbi_platform.h
+++ b/include/sbi/sbi_platform.h
@@ -48,6 +48,7 @@
 #include <sbi/sbi_error.h>
 #include <sbi/sbi_scratch.h>
 #include <sbi/sbi_version.h>
+#include <sbi/sbi_trap_ldst.h>
 
 struct sbi_domain_memregion;
 struct sbi_ecall_return;
@@ -683,6 +684,50 @@ static inline int sbi_platform_vendor_ext_provider(
 	return SBI_ENOTSUPP;
 }
 
+/**
+ * Ask platform to emulate the trapped load
+ *
+ * @param plat pointer to struct sbi_platform
+ * @param rlen length of the load: 1/2/4/8...
+ * @param addr virtual address of the load. Platform needs to page-walk and
+ *        find the physical address if necessary
+ * @param out_val value loaded
+ *
+ * @return 0 on success and negative error code on failure
+ */
+static inline int sbi_platform_emulate_load(const struct sbi_platform *plat,
+					    int rlen, unsigned long addr,
+					    union sbi_ldst_data *out_val)
+{
+	if (plat && sbi_platform_ops(plat)->emulate_load) {
+		return sbi_platform_ops(plat)->emulate_load(rlen, addr,
+							    out_val);
+	}
+	return SBI_ENOTSUPP;
+}
+
+/**
+ * Ask platform to emulate the trapped store
+ *
+ * @param plat pointer to struct sbi_platform
+ * @param wlen length of the store: 1/2/4/8...
+ * @param addr virtual address of the store. Platform needs to page-walk and
+ *        find the physical address if necessary
+ * @param in_val value to store
+ *
+ * @return 0 on success and negative error code on failure
+ */
+static inline int sbi_platform_emulate_store(const struct sbi_platform *plat,
+					     int wlen, unsigned long addr,
+					     union sbi_ldst_data in_val)
+{
+	if (plat && sbi_platform_ops(plat)->emulate_store) {
+		return sbi_platform_ops(plat)->emulate_store(wlen, addr,
+							     in_val);
+	}
+	return SBI_ENOTSUPP;
+}
+
 #endif
 
 #endif
diff --git a/lib/sbi/sbi_trap_ldst.c b/lib/sbi/sbi_trap_ldst.c
index b9dc7ea..d864ad1 100644
--- a/lib/sbi/sbi_trap_ldst.c
+++ b/lib/sbi/sbi_trap_ldst.c
@@ -15,6 +15,7 @@
 #include <sbi/sbi_pmu.h>
 #include <sbi/sbi_trap.h>
 #include <sbi/sbi_unpriv.h>
+#include <sbi/sbi_platform.h>
 
 /**
  * Load emulator callback:
@@ -319,14 +320,46 @@ int sbi_misaligned_store_handler(struct sbi_trap_regs *regs,
 				      sbi_misaligned_st_emulator);
 }
 
+static int sbi_ld_access_emulator(int rlen, union sbi_ldst_data *out_val,
+				  struct sbi_trap_regs *regs,
+				  const struct sbi_trap_info *orig_trap)
+{
+	/* If fault came from M mode, just fail */
+	if (((regs->mstatus & MSTATUS_MPP) >> MSTATUS_MPP_SHIFT) == PRV_M)
+		return SBI_EINVAL;
+
+	/* If platform emulator failed, we redirect instead of fail */
+	if (sbi_platform_emulate_load(sbi_platform_thishart_ptr(), rlen,
+				      orig_trap->tval, out_val))
+		return sbi_trap_redirect(regs, orig_trap);
+
+	return rlen;
+}
+
 int sbi_load_access_handler(struct sbi_trap_regs *regs,
 			    const struct sbi_trap_info *orig_trap)
 {
-	return sbi_trap_redirect(regs, orig_trap);
+	return sbi_trap_emulate_load(regs, orig_trap, sbi_ld_access_emulator);
+}
+
+static int sbi_st_access_emulator(int wlen, union sbi_ldst_data in_val,
+				  struct sbi_trap_regs *regs,
+				  const struct sbi_trap_info *orig_trap)
+{
+	/* If fault came from M mode, just fail */
+	if (((regs->mstatus & MSTATUS_MPP) >> MSTATUS_MPP_SHIFT) == PRV_M)
+		return SBI_EINVAL;
+
+	/* If platform emulator failed, we redirect instead of fail */
+	if (sbi_platform_emulate_store(sbi_platform_thishart_ptr(), wlen,
+				       orig_trap->tval, in_val))
+		return sbi_trap_redirect(regs, orig_trap);
+
+	return wlen;
 }
 
 int sbi_store_access_handler(struct sbi_trap_regs *regs,
 			     const struct sbi_trap_info *orig_trap)
 {
-	return sbi_trap_redirect(regs, orig_trap);
+	return sbi_trap_emulate_store(regs, orig_trap, sbi_st_access_emulator);
 }