[PATCH] Add commands for reading and writing raw bytes to CMOS

From: Vladimir Serbinenko <phcoder@gmail.com>
To: grub-devel@gnu.org
Cc: Vladimir Serbinenko <phcoder@gmail.com>
Subject: [PATCH] Add commands for reading and writing raw bytes to CMOS
Date: Fri, 17 May 2024 00:39:49 +0300	[thread overview]
Message-ID: <20240516213949.978-1-phcoder@gmail.com> (raw)

With some coreboot configs setting a byte to a magic value
changes behaviour on next boot. Setting bit-by-bit is
possible but not convenient. Add cmosread and cmoswrite for
convenience.

Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
---
 grub-core/commands/i386/cmostest.c | 72 +++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

diff --git a/grub-core/commands/i386/cmostest.c b/grub-core/commands/i386/cmostest.c
index 1f0c5341d..814df0f43 100644
--- a/grub-core/commands/i386/cmostest.c
+++ b/grub-core/commands/i386/cmostest.c
@@ -18,9 +18,12 @@
 
 #include <grub/dl.h>
 #include <grub/command.h>
+#include <grub/extcmd.h>
 #include <grub/misc.h>
 #include <grub/cmos.h>
 #include <grub/i18n.h>
+#include <grub/mm.h>
+#include <grub/env.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -99,7 +102,66 @@ grub_cmd_cmosset (struct grub_command *cmd __attribute__ ((unused)),
   return grub_cmos_write (byte, value | (1 << bit));
 }
 
-static grub_command_t cmd, cmd_clean, cmd_set;
+static grub_err_t
+grub_cmd_cmoswrite (struct grub_command *cmd __attribute__ ((unused)),
+		    int argc, char *argv[])
+{
+  unsigned long byte, value;
+  const char *end;
+
+  if (argc != 2)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments expected"));
+
+  byte = grub_strtoul (argv[0], &end, 0);
+  if (byte >= 0x100 || argv[0][0] == '\0' || *end != '\0')
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid address"));
+
+  value = grub_strtoul (argv[1], &end, 0);
+  if (value >= 0x100 || argv[1][0] == '\0' || *end != '\0')
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid value"));
+
+  return grub_cmos_write (byte, value);
+}
+
+static grub_err_t
+grub_cmd_cmosread (grub_extcmd_context_t ctxt, int argc, char **argv)
+{
+  unsigned long byte;
+  grub_uint8_t value = 0;
+  grub_err_t err;
+  const char *end;
+
+  if (argc != 1)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument expected"));
+
+  byte = grub_strtoul (argv[0], &end, 0);
+  if (byte >= 0x100 || argv[0][0] == '\0' || *end != '\0')
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid address"));
+
+  err = grub_cmos_read (byte, &value);
+  if (err)
+    return err;
+
+  if (ctxt->state[0].set)
+    {
+      char buf[sizeof ("XX")];
+      grub_snprintf (buf, sizeof (buf), "%x", value);
+      grub_env_set(ctxt->state[0].arg, buf);
+    }
+  else
+    grub_printf_("CMOS value at 0x%lx is 0x%x\n", byte, value);
+  return GRUB_ERR_NONE;
+}
+
+static const struct grub_arg_option read_options[] =
+  {
+    {0, 's', 0, N_("Save read value into variable VARNAME."),
+     N_("VARNAME"), ARG_TYPE_STRING},
+    {0, 0, 0, 0, 0, 0}
+  };
+
+static grub_command_t cmd, cmd_clean, cmd_set, cmd_write;
+static grub_extcmd_t cmd_read;
 
 \f
 GRUB_MOD_INIT(cmostest)
@@ -114,6 +176,12 @@ GRUB_MOD_INIT(cmostest)
 				   N_("BYTE:BIT"),
 				   /* TRANSLATORS: A bit may be either set (1) or clear (0).  */
 				   N_("Set bit at BYTE:BIT in CMOS."));
+  cmd_read = grub_register_extcmd_lockdown ("cmosread", grub_cmd_cmosread, 0,
+				       N_("[-s VAR] ADDR"),
+				       N_("Read CMOS byte at ADDR."), read_options);
+  cmd_write = grub_register_command_lockdown ("cmoswrite", grub_cmd_cmoswrite,
+					      N_("ADDR VALUE"),
+					      N_("Set CMOS byte at ADDR to VALUE."));
 }
 
 GRUB_MOD_FINI(cmostest)
@@ -121,4 +189,6 @@ GRUB_MOD_FINI(cmostest)
   grub_unregister_command (cmd);
   grub_unregister_command (cmd_clean);
   grub_unregister_command (cmd_set);
+  grub_unregister_extcmd (cmd_read);
+  grub_unregister_command (cmd_write);
 }
-- 
2.39.2


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