On 2019/7/29 19:38, Christophe Leroy wrote:

Le 17/07/2019 à 10:06, Jason Yan a écrit :

quoted

One may want to disable kaslr when boot, so provide a cmdline parameter
'nokaslr' to support this.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Cc: Diana Craciun <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Kees Cook <redacted>
---
  arch/powerpc/kernel/kaslr_booke.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/kernel/kaslr_booke.c 

b/arch/powerpc/kernel/kaslr_booke.c
index 00339c05879f..e65a5d9d2ff1 100644

--- a/arch/powerpc/kernel/kaslr_booke.c
+++ b/arch/powerpc/kernel/kaslr_booke.c

@@ -373,6 +373,18 @@ static unsigned long __init 

kaslr_choose_location(void *dt_ptr, phys_addr_t size
      return kaslr_offset;
  }
+static inline __init bool kaslr_disabled(void)
+{
+    char *str;
+
+    str = strstr(early_command_line, "nokaslr");

Why using early_command_line instead of boot_command_line ?

Will switch to boot_command_line.

quoted

+    if ((str == early_command_line) ||
+        (str > early_command_line && *(str - 1) == ' '))

Is that stuff really needed ?

Why not just:

return strstr(early_command_line, "nokaslr") != NULL;

This code is derived from other arch such as arm64/mips. It's trying to
make sure that 'nokaslr' is a separate word but not part of other words 
such as 'abcnokaslr'.

quoted

+        return true;
+
+    return false;
+}

quoted

+
  /*
   * To see if we need to relocate the kernel to a random offset
   * void *dt_ptr - address of the device tree

@@ -388,6 +400,8 @@ notrace void __init kaslr_early_init(void *dt_ptr, 

phys_addr_t size)
      kernel_sz = (unsigned long)_end - KERNELBASE;
      kaslr_get_cmdline(dt_ptr);
+    if (kaslr_disabled())
+        return;
      offset = kaslr_choose_location(dt_ptr, size, kernel_sz);

Christophe

.