[PATCH 0/2] lib: sbi: Fix stale trap_context/prev_context linking

[PATCH 0/2] lib: sbi: Fix stale trap_context/prev_context linking

[Nia Su]

Patch 1 clears scratch->trap_context on warm boot, since
non-retentive suspend/resume jumps straight there without restoring
it, leaving a stale pointer misused as the next trap's prev_context.

Patch 2 fixes sbi_trap_rnmi_handler() to link prev_context on entry
and restore it on exit, the same way sbi_trap_handler() does.

Signed-off-by: Nia Su <nia.su@sifive.com>
---
Nia Su (2):
      firmware: Clear scratch->trap_context on warm boot
      lib: sbi: Fix stale prev_context in RNMI handler

 firmware/fw_base.S |  3 +++
 lib/sbi/sbi_trap.c | 10 ++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)
---
base-commit: 35511bc6ee1c9c17b6a89b44c52e2044bb51b979
change-id: 20260902-trap-context-fix-b9e78441953e

--


-- 
opensbi mailing list
opensbi@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/opensbi

[PATCH 1/2] firmware: Clear scratch->trap_context on warm boot

[Nia Su]

sbi_trap_handler() links tcntx->prev_context on entry and restores
scratch->trap_context on exit, forming a stack that unwinds through
the same path it was pushed from.

Non-retentive suspend/resume breaks that unwind: the SBI call
requesting suspend jumps straight to warm boot (jump_warmboot())
instead of returning through the normal exit path, leaving
scratch->trap_context stale. Since each hart's scratch space sits at
a fixed address, the next trap taken after warm boot resume reads
that same stale scratch->trap_context as its prev_context.

Clear trap_context in the scratch space on warm boot entry,
mirroring what cold boot's _scratch_init already does.

Signed-off-by: Nia Su <nia.su@sifive.com>
---
 firmware/fw_base.S | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/firmware/fw_base.S b/firmware/fw_base.S
index 0c5c65c10e5cf38d1cc6d0b3a66ffac661e7bacf..8ccca5e91c09f9c4cfcbab9c31c7e77afe7a96ab 100644
--- a/firmware/fw_base.S
+++ b/firmware/fw_base.S
@@ -364,6 +364,9 @@ _start_warm:
 	/* update the mscratch */
 	csrw	CSR_MSCRATCH, tp
 
+	/* Clear trap_context in scratch space */
+	REG_S	zero, SBI_SCRATCH_TRAP_CONTEXT_OFFSET(tp)
+
 	/* Setup stack */
 	add	sp, tp, zero
 

-- 
2.43.7


-- 
opensbi mailing list
opensbi@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/opensbi

[PATCH 2/2] lib: sbi: Fix stale prev_context in RNMI handler

[Nia Su]

An earlier SBI trap may have already used the same M-mode exception
stack slot to save its trap context before an RNMI is taken.
sbi_trap_rnmi_handler() never initializes prev_context before
sbi_trap_error() walks it to print trap diagnostics, so it can read
whatever stale value happens to be left in that slot.

Link prev_context on entry and restore it on exit, the same way
sbi_trap_handler() does. This also lets an exception taken while
already inside RNMI handling chain back to the RNMI's own trap
context instead of dropping it, so sbi_trap_error() prints every
nested context correctly, including the RNMI's.

Fixes: 00fec20b4976 ("firmware: Add RNMI handler infrastructure")
Suggested-by: Nick Hu <nick.hu@sifive.com>
Signed-off-by: Nia Su <nia.su@sifive.com>
---
 lib/sbi/sbi_trap.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/sbi/sbi_trap.c b/lib/sbi/sbi_trap.c
index 16774fd2f73059c1268bfb9f43fdf8e9c460c0b6..e694188c25b7b1715df660206af0a501290389fc 100644
--- a/lib/sbi/sbi_trap.c
+++ b/lib/sbi/sbi_trap.c
@@ -394,9 +394,14 @@ trap_done:
 struct sbi_trap_context *sbi_trap_rnmi_handler(struct sbi_trap_context *tcntx)
 {
 	int rc;
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
 	const struct sbi_platform *plat = sbi_platform_thishart_ptr();
 	const struct sbi_platform_operations *ops = sbi_platform_ops(plat);
 
+	/* Update trap context pointer so nested traps chain correctly */
+	tcntx->prev_context = sbi_trap_get_context(scratch);
+	sbi_trap_set_context(scratch, tcntx);
+
 	/* Call platform-specific NMI handler if registered */
 	if (ops && ops->rnmi_handler) {
 		rc = ops->rnmi_handler(tcntx);
@@ -404,14 +409,15 @@ struct sbi_trap_context *sbi_trap_rnmi_handler(struct sbi_trap_context *tcntx)
 			/* Platform handler failed to handle NMI */
 			sbi_trap_error("platform NMI handler failed", rc, tcntx);
 		}
-		return tcntx;
+		goto done;
 	}
 
 	/* No platform handler - treat as unhandled NMI */
 	sbi_trap_error("unhandled NMI (no platform rnmi_handler)",
 		       SBI_ENOTSUPP, tcntx);
 
-	/* Never returns */
+done:
+	sbi_trap_set_context(scratch, tcntx->prev_context);
 	return tcntx;
 }
 

-- 
2.43.7


-- 
opensbi mailing list
opensbi@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/opensbi