Re: [tip:efi/core] efibc: Add EFI Bootloader Control module

Compostella, Jeremy
2016-04-29T13:55:00Z

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Matt Fleming <matt@codeblueprint.co.uk> writes:

> On Fri, 29 Apr, at 01:36:01PM, Jeremy Compostella wrote:
>> I would go for this last proposal because it fixes the issue, it works
>> with the potential race condition you mentioned and it is a simple
>> solution. Yet, it means that if we really run into a race condition,
>> the LoaderEntryOneShot value might be indeterminate.
>>
>> Though, this is a very unlikely situation and if it happens I cannot
>> think of any good reason to prefer to store the first restart target
>> or the second.
>>
>> Do you want me to make this change ?
>
> Yes please, that'd be greatly appreciated. Be sure to do it on top of
> either the EFI 'next' branch or tip:efi/core.
Please, find the patch in attachment. I wrote it on top of
tip:efi/core.

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>From ef3a2941769e59b11d1ec36117209dc4c90c7cf9 Mon Sep 17 00:00:00 2001
From: Jeremy Compostella <jeremy.compostella@intel.com>
Date: Fri, 29 Apr 2016 15:29:59 +0200
Subject: [PATCH] efibc: fix excessive stack footprint warning

Use dynamic memory allocation instead of stack memory for the entry
object.

This patch also fixes a potential buffer override.

Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
---
drivers/firmware/efi/efibc.c | 36 ++++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/efi/efibc.c b/drivers/firmware/efi/efibc.c
index 2e0c7cc..dd6d1a6 100644
--- a/drivers/firmware/efi/efibc.c
+++ b/drivers/firmware/efi/efibc.c
@@ -17,6 +17,7 @@
#include <linux/efi.h>
#include <linux/module.h>
#include <linux/reboot.h>
+#include <linux/slab.h>

static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
{
@@ -28,42 +29,53 @@ static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
str16[i] = '\0';
}

-static void efibc_set_variable(const char *name, const char *value)
+static int efibc_set_variable(const char *name, const char *value)
{
int ret;
efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
- struct efivar_entry entry;
+ struct efivar_entry *entry;
size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);

- if (size > sizeof(entry.var.Data))
+ if (size > sizeof(entry->var.Data)) {
pr_err("value is too large");
+ return -1;
+ }

- efibc_str_to_str16(name, entry.var.VariableName);
- efibc_str_to_str16(value, (efi_char16_t *)entry.var.Data);
- memcpy(&entry.var.VendorGuid, &guid, sizeof(guid));
+ entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+ if (!entry) {
+ pr_err("failed to allocate efivar entry");
+ return -1;
+ }

- ret = efivar_entry_set(&entry,
+ efibc_str_to_str16(name, entry->var.VariableName);
+ efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
+ memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
+
+ ret = efivar_entry_set(entry,
EFI_VARIABLE_NON_VOLATILE
| EFI_VARIABLE_BOOTSERVICE_ACCESS
| EFI_VARIABLE_RUNTIME_ACCESS,
- size, entry.var.Data, NULL);
+ size, entry->var.Data, NULL);
if (ret)
pr_err("failed to set %s EFI variable: 0x%x\n",
name, ret);
+
+ kfree(entry);
+ return ret;
}

static int efibc_reboot_notifier_call(struct notifier_block *notifier,
unsigned long event, void *data)
{
const char *reason = "shutdown";
+ int ret;

if (event == SYS_RESTART)
reason = "reboot";

- efibc_set_variable("LoaderEntryRebootReason", reason);
-
- if (!data)
- return NOTIFY_DONE;
+ ret = efibc_set_variable("LoaderEntryRebootReason", reason);
+ if (ret || !data)
+ return NOTIFY_DONE;

efibc_set_variable("LoaderEntryOneShot", (char *)data);

--
1.9.1

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Jérémy
--
One Emacs to rule them all