Even though it is documented how to specifiy efi parameters, it is
possible to cause a kernel panic due to a derreference of a NULL pointer when
parsing such parameters if "efi" alone is given:
PANIC: early exception 0e rip 10:ffffffff812fb361 error 0 cr2 0
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.2.0-rc1+ #450
[ 0.000000] ffffffff81fe20a9 ffffffff81e03d50 ffffffff8184bb0f 00000000000003f8
[ 0.000000] 0000000000000000 ffffffff81e03e08 ffffffff81f371a1 64656c62616e6520
[ 0.000000] 0000000000000069 000000000000005f 0000000000000000 0000000000000000
[ 0.000000] Call Trace:
[ 0.000000] [<ffffffff8184bb0f>] dump_stack+0x45/0x57
[ 0.000000] [<ffffffff81f371a1>] early_idt_handler_common+0x81/0xae
[ 0.000000] [<ffffffff812fb361>] ? parse_option_str+0x11/0x90
[ 0.000000] [<ffffffff81f4dd69>] arch_parse_efi_cmdline+0x15/0x42
[ 0.000000] [<ffffffff81f376e1>] do_early_param+0x50/0x8a
[ 0.000000] [<ffffffff8106b1b3>] parse_args+0x1e3/0x400
[ 0.000000] [<ffffffff81f37a43>] parse_early_options+0x24/0x28
[ 0.000000] [<ffffffff81f37691>] ? loglevel+0x31/0x31
[ 0.000000] [<ffffffff81f37a78>] parse_early_param+0x31/0x3d
[ 0.000000] [<ffffffff81f3ae98>] setup_arch+0x2de/0xc08
[ 0.000000] [<ffffffff8109629a>] ? vprintk_default+0x1a/0x20
[ 0.000000] [<ffffffff81f37b20>] start_kernel+0x90/0x423
[ 0.000000] [<ffffffff81f37495>] x86_64_start_reservations+0x2a/0x2c
[ 0.000000] [<ffffffff81f37582>] x86_64_start_kernel+0xeb/0xef
[ 0.000000] RIP 0xffffffff81ba2efc
This panic is not reproducible with "efi=" as this will result in a non-NULL
zero-lenght string.
Thus, verify that the pointer to the parameter string is not NULL. This is
consistent with other parameter-parsing functions which check for NULL pointers.
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v1:
- Include a stackdump showing the code path to the panic
- Describe further in which scenarios the panic can be reproduced
- Describe more accurately the fix.
arch/x86/platform/efi/efi.c | 4 ++++
drivers/firmware/efi/efi.c | 4 ++++
2 files changed, 8 insertions(+)
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index cfba30f..d323e3a 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -972,6 +972,10 @@ u64 efi_mem_attributes(unsigned long phys_addr)
static int __init arch_parse_efi_cmdline(char *str)
{
+ if (!str) {
+ pr_warn("need at least one option\n");
+ return -EINVAL;
+ }
if (parse_option_str(str, "old_map"))
set_bit(EFI_OLD_MEMMAP, &efi.flags);
if (parse_option_str(str, "debug"))
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 46eb8a6..9816e3d 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -58,6 +58,10 @@ bool efi_runtime_disabled(void)
static int __init parse_efi_cmdline(char *str)
{
+ if (!str) {
+ pr_warn("need at least one option\n");
+ return -EINVAL;
+ }
if (parse_option_str(str, "noruntime"))
disable_runtime = true;
--
1.9.1
--
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