[PATCH bpf-next v2 1/3] riscv: extend patch_text_nosync() for multiple pages

Puranjay Mohan
2023-08-24T13:31:41Z

The patch_insn_write() function currently doesn't work for multiple
pages of instructions, therefore patch_text_nosync() will fail with a
page fault if called with lengths spanning multiple pages.

This commit extends the patch_insn_write() function to support multiple
pages by copying at max 2 pages at a time in a loop. This implementation
is similar to text_poke_copy() function of x86.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
---
arch/riscv/kernel/patch.c | 39 ++++++++++++++++++++++++++++++++++-----
1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 575e71d6c8ae..465b2eebbc37 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -53,12 +53,18 @@ static void patch_unmap(int fixmap)
}
NOKPROBE_SYMBOL(patch_unmap);

-static int patch_insn_write(void *addr, const void *insn, size_t len)
+static int __patch_insn_write(void *addr, const void *insn, size_t len)
{
void *waddr = addr;
bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
int ret;

+ /*
+ * Only two pages can be mapped at a time for writing.
+ */
+ if (len > 2 * PAGE_SIZE)
+ return -EINVAL;
+
/*
* Before reaching here, it was expected to lock the text_mutex
* already, so we don't need to give another lock here and could
@@ -74,7 +80,7 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
lockdep_assert_held(&text_mutex);

if (across_pages)
- patch_map(addr + len, FIX_TEXT_POKE1);
+ patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);

waddr = patch_map(addr, FIX_TEXT_POKE0);

@@ -87,15 +93,38 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)

return ret;
}
-NOKPROBE_SYMBOL(patch_insn_write);
+NOKPROBE_SYMBOL(__patch_insn_write);
#else
-static int patch_insn_write(void *addr, const void *insn, size_t len)
+static int __patch_insn_write(void *addr, const void *insn, size_t len)
{
return copy_to_kernel_nofault(addr, insn, len);
}
-NOKPROBE_SYMBOL(patch_insn_write);
+NOKPROBE_SYMBOL(__patch_insn_write);
#endif /* CONFIG_MMU */

+static int patch_insn_write(void *addr, const void *insn, size_t len)
+{
+ size_t patched = 0;
+ size_t size;
+ int ret = 0;
+
+ /*
+ * Copy the instructions to the destination address, two pages at a time
+ * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
+ */
+ while (patched < len && !ret) {
+ size = min_t(size_t,
+ PAGE_SIZE * 2 - offset_in_page(addr + patched),
+ len - patched);
+ ret = __patch_insn_write(addr + patched, insn + patched, size);
+
+ patched += size;
+ }
+
+ return ret;
+}
+NOKPROBE_SYMBOL(patch_insn_write);
+
int patch_text_nosync(void *addr, const void *insns, size_t len)
{
u32 *tp = addr;
--
2.39.2