[PATCH fixes v2 2/2] riscv: uprobes: Add missing fence.i after building the XOL buffer

[Björn Töpel]

From: Björn Töpel <bj...@rivosinc.com>

The XOL (execute out-of-line) buffer is used to single-step the
replaced instruction(s) for uprobes. The RISC-V port was missing a
proper fence.i (i$ flushing) after constructing the XOL buffer, which
can result in incorrect execution of stale/broken instructions.

This was found running the BPF selftests "test_progs:
uprobe_autoattach, attach_probe" on the Spacemit K1/X60, where the
uprobes tests randomly blew up.

Reviewed-by: Guo Ren <guo...@kernel.org>
Fixes: 74784081aac8 ("riscv: Add uprobes supported")
Signed-off-by: Björn Töpel <bj...@rivosinc.com>
---
v2: Correct flush range (Samuel)
---
 arch/riscv/kernel/probes/uprobes.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kernel/probes/uprobes.c 
b/arch/riscv/kernel/probes/uprobes.c
index 4b3dc8beaf77..cc15f7ca6cc1 100644
--- a/arch/riscv/kernel/probes/uprobes.c
+++ b/arch/riscv/kernel/probes/uprobes.c
@@ -167,6 +167,7 @@ void arch_uprobe_copy_ixol(struct page *page, unsigned long 
vaddr,
        /* Initialize the slot */
        void *kaddr = kmap_atomic(page);
        void *dst = kaddr + (vaddr & ~PAGE_MASK);
+       unsigned long start = (unsigned long)dst;
 
        memcpy(dst, src, len);
 
@@ -176,13 +177,6 @@ void arch_uprobe_copy_ixol(struct page *page, unsigned 
long vaddr,
                *(uprobe_opcode_t *)dst = __BUG_INSN_32;
        }
 
+       flush_icache_range(start, start + len);
        kunmap_atomic(kaddr);
-
-       /*
-        * We probably need flush_icache_user_page() but it needs vma.
-        * This should work on most of architectures by default. If
-        * architecture needs to do something different it can define
-        * its own version of the function.
-        */
-       flush_dcache_page(page);
 }
-- 
2.45.2