[PATCH 5.15 58/91] riscv: add icache flush for nommu sigreturn trampoline

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From: Mathis Salmen <mathis.salmen@xxxxxxxxx>

commit 8d736482749f6d350892ef83a7a11d43cd49981e upstream.

In a NOMMU kernel, sigreturn trampolines are generated on the user
stack by setup_rt_frame. Currently, these trampolines are not instruction
fenced, thus their visibility to ifetch is not guaranteed.

This patch adds a flush_icache_range in setup_rt_frame to fix this
problem.

Signed-off-by: Mathis Salmen <mathis.salmen@xxxxxxxxx>
Fixes: 6bd33e1ece52 ("riscv: add nommu support")
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230406101130.82304-1-mathis.salmen@xxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/riscv/kernel/signal.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -16,6 +16,7 @@
 #include <asm/vdso.h>
 #include <asm/switch_to.h>
 #include <asm/csr.h>
+#include <asm/cacheflush.h>
 
 extern u32 __user_rt_sigreturn[2];
 
@@ -178,6 +179,7 @@ static int setup_rt_frame(struct ksignal
 {
 	struct rt_sigframe __user *frame;
 	long err = 0;
+	unsigned long __maybe_unused addr;
 
 	frame = get_sigframe(ksig, regs, sizeof(*frame));
 	if (!access_ok(frame, sizeof(*frame)))
@@ -206,7 +208,12 @@ static int setup_rt_frame(struct ksignal
 	if (copy_to_user(&frame->sigreturn_code, __user_rt_sigreturn,
 			 sizeof(frame->sigreturn_code)))
 		return -EFAULT;
-	regs->ra = (unsigned long)&frame->sigreturn_code;
+
+	addr = (unsigned long)&frame->sigreturn_code;
+	/* Make sure the two instructions are pushed to icache. */
+	flush_icache_range(addr, addr + sizeof(frame->sigreturn_code));
+
+	regs->ra = addr;
 #endif /* CONFIG_MMU */
 
 	/*





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