riscv: implement a memset like function for text

The BPF JIT needs to write invalid instructions to RX regions of memory to
invalidate removed BPF programs. This needs a function like memset() that
can work with RX memory.

Implement patch_text_set_nosync() which is similar to text_poke_set() of
x86.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20230831131229.497941-4-puranjay12@gmail.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/include/asm/patch.h b/arch/riscv/include/asm/patch.h
index 63c98833d5105d325db88ab3a232462fc0bdae85..e88b52d39eac76bc8d5658a2f65bda8f9d260f08 100644 (file)
--- a/arch/riscv/include/asm/patch.h
+++ b/arch/riscv/include/asm/patch.h
@@ -7,6 +7,7 @@
 #define _ASM_RISCV_PATCH_H
 
 int patch_text_nosync(void *addr, const void *insns, size_t len);
+int patch_text_set_nosync(void *addr, u8 c, size_t len);
 int patch_text(void *addr, u32 *insns, int ninsns);
 
 extern int riscv_patch_in_stop_machine;

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 2c97e246f4dc36603f0e89f13c4633b3cebb880b..13ee7bf589a15e1fed201415dbe352494c1ba526 100644 (file)
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -6,6 +6,7 @@
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/memory.h>
+#include <linux/string.h>
 #include <linux/uaccess.h>
 #include <linux/stop_machine.h>
 #include <asm/kprobes.h>
@@ -53,6 +54,39 @@ static void patch_unmap(int fixmap)
 }
 NOKPROBE_SYMBOL(patch_unmap);
 
+static int __patch_insn_set(void *addr, u8 c, size_t len)
+{
+       void *waddr = addr;
+       bool across_pages = (((uintptr_t)addr & ~PAGE_MASK) + len) > PAGE_SIZE;
+
+       /*
+        * 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
+        * ensure that it was safe between each cores.
+        */
+       lockdep_assert_held(&text_mutex);
+
+       if (across_pages)
+               patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
+
+       waddr = patch_map(addr, FIX_TEXT_POKE0);
+
+       memset(waddr, c, len);
+
+       patch_unmap(FIX_TEXT_POKE0);
+
+       if (across_pages)
+               patch_unmap(FIX_TEXT_POKE1);
+
+       return 0;
+}
+NOKPROBE_SYMBOL(__patch_insn_set);
+
 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 {
        void *waddr = addr;
@@ -95,6 +129,14 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
 }
 NOKPROBE_SYMBOL(__patch_insn_write);
 #else
+static int __patch_insn_set(void *addr, u8 c, size_t len)
+{
+       memset(addr, c, len);
+
+       return 0;
+}
+NOKPROBE_SYMBOL(__patch_insn_set);
+
 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 {
        return copy_to_kernel_nofault(addr, insn, len);
@@ -102,6 +144,41 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
 NOKPROBE_SYMBOL(__patch_insn_write);
 #endif /* CONFIG_MMU */
 
+static int patch_insn_set(void *addr, u8 c, size_t len)
+{
+       size_t patched = 0;
+       size_t size;
+       int ret = 0;
+
+       /*
+        * __patch_insn_set() can only work on 2 pages at a time so call it in a
+        * loop with 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_set(addr + patched, c, size);
+
+               patched += size;
+       }
+
+       return ret;
+}
+NOKPROBE_SYMBOL(patch_insn_set);
+
+int patch_text_set_nosync(void *addr, u8 c, size_t len)
+{
+       u32 *tp = addr;
+       int ret;
+
+       ret = patch_insn_set(tp, c, len);
+
+       if (!ret)
+               flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
+
+       return ret;
+}
+NOKPROBE_SYMBOL(patch_text_set_nosync);
+
 static int patch_insn_write(void *addr, const void *insn, size_t len)
 {
        size_t patched = 0;