riscv: extend patch_text_nosync() for multiple pages

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: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20230831131229.497941-3-puranjay12@gmail.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 575e71d6c8ae2d0b4e9b0935f117299884272a80..2c97e246f4dc36603f0e89f13c4633b3cebb880b 100644 (file)
--- 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 + offset_in_page(addr) > 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 +93,36 @@ 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;