* [PATCH] LoongArch: kexec: Fix address space mismatch in command line lookup
@ 2026-06-26 10:38 George Guo
0 siblings, 0 replies; 3+ messages in thread
From: George Guo @ 2026-06-26 10:38 UTC (permalink / raw)
To: Huacai Chen; +Cc: WANG Xuerui, Qiang Ma, Kexin Liu, loongarch, linux-kernel
From: George Guo <guodongtai@kylinos.cn>
When searching the loaded segments for the "kexec" command line marker,
the kexec_load(2) path (file_mode == 0) passes the user-space segment
buffer straight to strncmp() through a bogus (char __user *) cast. This
dereferences a user pointer in kernel context, which is wrong and is
flagged by sparse:
arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in
argument 2 (different address spaces) @@ expected char const * @@ got
char [noderef] __user *
Copy the marker-sized prefix of each segment into a small on-stack
buffer with copy_from_user() before comparing, and skip segments that
fault. The subsequent copy_from_user() that stages the full command line
into the safe area is left unchanged.
Fixes: 4a03b2ac06a5 ("LoongArch: Add kexec support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605051639.aEPioXdD-lkp@intel.com/
Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
arch/loongarch/kernel/machine_kexec.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index d7fafda1d541..6f563175ddbf 100644
--- a/arch/loongarch/kernel/machine_kexec.c
+++ b/arch/loongarch/kernel/machine_kexec.c
@@ -42,7 +42,7 @@ static unsigned long first_ind_entry;
int machine_kexec_prepare(struct kimage *kimage)
{
int i;
- char *bootloader = "kexec";
+ static const char bootloader[] = "kexec";
void *cmdline_ptr = (void *)KEXEC_CMDLINE_ADDR;
kimage->arch.efi_boot = fw_arg0;
@@ -57,9 +57,13 @@ int machine_kexec_prepare(struct kimage *kimage)
strlen((char *)kimage->arch.cmdline_ptr) + 1);
kimage->arch.cmdline_ptr = (unsigned long)KEXEC_CMDLINE_ADDR;
} else {
+ char tmp[sizeof(bootloader)];
+
/* Find the command line */
for (i = 0; i < kimage->nr_segments; i++) {
- if (!strncmp(bootloader, (char __user *)kimage->segment[i].buf, strlen(bootloader))) {
+ if (copy_from_user(tmp, kimage->segment[i].buf, strlen(bootloader)))
+ continue;
+ if (!strncmp(bootloader, tmp, strlen(bootloader))) {
if (!copy_from_user(cmdline_ptr, kimage->segment[i].buf, COMMAND_LINE_SIZE))
kimage->arch.cmdline_ptr = (unsigned long)cmdline_ptr;
break;
--
2.25.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] LoongArch: kexec: Fix address space mismatch in command line lookup
2026-06-26 10:51 George Guo
@ 2026-06-30 8:25 ` Huacai Chen
0 siblings, 0 replies; 3+ messages in thread
From: Huacai Chen @ 2026-06-30 8:25 UTC (permalink / raw)
To: George Guo
Cc: WANG Xuerui, Qiang Ma, loongarch, linux-kernel, George Guo,
kernel test robot, Kexin Liu
Hi, George,
On Fri, Jun 26, 2026 at 6:52 PM George Guo <dongtai.guo@linux.dev> wrote:
>
> From: George Guo <guodongtai@kylinos.cn>
>
> When searching the loaded segments for the "kexec" command line marker,
> the kexec_load(2) path (file_mode == 0) passes the user-space segment
> buffer straight to strncmp() through a bogus (char __user *) cast. This
> dereferences a user pointer in kernel context, which is wrong and is
> flagged by sparse:
>
> arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in
> argument 2 (different address spaces) @@ expected char const * @@ got
> char [noderef] __user *
>
> Copy the marker-sized prefix of each segment into a small on-stack
> buffer with copy_from_user() before comparing, and skip segments that
> fault. The subsequent copy_from_user() that stages the full command line
> into the safe area is left unchanged.
>
> Fixes: 4a03b2ac06a5 ("LoongArch: Add kexec support")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605051639.aEPioXdD-lkp@intel.com/
> Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
> Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
> Signed-off-by: George Guo <guodongtai@kylinos.cn>
> ---
> arch/loongarch/kernel/machine_kexec.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> index d7fafda1d541..6f563175ddbf 100644
> --- a/arch/loongarch/kernel/machine_kexec.c
> +++ b/arch/loongarch/kernel/machine_kexec.c
> @@ -42,7 +42,7 @@ static unsigned long first_ind_entry;
> int machine_kexec_prepare(struct kimage *kimage)
> {
> int i;
> - char *bootloader = "kexec";
> + static const char bootloader[] = "kexec";
> void *cmdline_ptr = (void *)KEXEC_CMDLINE_ADDR;
>
> kimage->arch.efi_boot = fw_arg0;
> @@ -57,9 +57,13 @@ int machine_kexec_prepare(struct kimage *kimage)
> strlen((char *)kimage->arch.cmdline_ptr) + 1);
> kimage->arch.cmdline_ptr = (unsigned long)KEXEC_CMDLINE_ADDR;
> } else {
> + char tmp[sizeof(bootloader)];
Just define it as "head[8]" near bootloader, and bootloader is
unnecessary to modify.
Huacai
> +
> /* Find the command line */
> for (i = 0; i < kimage->nr_segments; i++) {
> - if (!strncmp(bootloader, (char __user *)kimage->segment[i].buf, strlen(bootloader))) {
> + if (copy_from_user(tmp, kimage->segment[i].buf, strlen(bootloader)))
> + continue;
> + if (!strncmp(bootloader, tmp, strlen(bootloader))) {
> if (!copy_from_user(cmdline_ptr, kimage->segment[i].buf, COMMAND_LINE_SIZE))
> kimage->arch.cmdline_ptr = (unsigned long)cmdline_ptr;
> break;
> --
> 2.25.1
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] LoongArch: kexec: Fix address space mismatch in command line lookup
@ 2026-06-26 10:51 George Guo
2026-06-30 8:25 ` Huacai Chen
0 siblings, 1 reply; 3+ messages in thread
From: George Guo @ 2026-06-26 10:51 UTC (permalink / raw)
To: Huacai Chen
Cc: WANG Xuerui, Qiang Ma, loongarch, linux-kernel, George Guo,
kernel test robot, Kexin Liu
From: George Guo <guodongtai@kylinos.cn>
When searching the loaded segments for the "kexec" command line marker,
the kexec_load(2) path (file_mode == 0) passes the user-space segment
buffer straight to strncmp() through a bogus (char __user *) cast. This
dereferences a user pointer in kernel context, which is wrong and is
flagged by sparse:
arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in
argument 2 (different address spaces) @@ expected char const * @@ got
char [noderef] __user *
Copy the marker-sized prefix of each segment into a small on-stack
buffer with copy_from_user() before comparing, and skip segments that
fault. The subsequent copy_from_user() that stages the full command line
into the safe area is left unchanged.
Fixes: 4a03b2ac06a5 ("LoongArch: Add kexec support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605051639.aEPioXdD-lkp@intel.com/
Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
arch/loongarch/kernel/machine_kexec.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index d7fafda1d541..6f563175ddbf 100644
--- a/arch/loongarch/kernel/machine_kexec.c
+++ b/arch/loongarch/kernel/machine_kexec.c
@@ -42,7 +42,7 @@ static unsigned long first_ind_entry;
int machine_kexec_prepare(struct kimage *kimage)
{
int i;
- char *bootloader = "kexec";
+ static const char bootloader[] = "kexec";
void *cmdline_ptr = (void *)KEXEC_CMDLINE_ADDR;
kimage->arch.efi_boot = fw_arg0;
@@ -57,9 +57,13 @@ int machine_kexec_prepare(struct kimage *kimage)
strlen((char *)kimage->arch.cmdline_ptr) + 1);
kimage->arch.cmdline_ptr = (unsigned long)KEXEC_CMDLINE_ADDR;
} else {
+ char tmp[sizeof(bootloader)];
+
/* Find the command line */
for (i = 0; i < kimage->nr_segments; i++) {
- if (!strncmp(bootloader, (char __user *)kimage->segment[i].buf, strlen(bootloader))) {
+ if (copy_from_user(tmp, kimage->segment[i].buf, strlen(bootloader)))
+ continue;
+ if (!strncmp(bootloader, tmp, strlen(bootloader))) {
if (!copy_from_user(cmdline_ptr, kimage->segment[i].buf, COMMAND_LINE_SIZE))
kimage->arch.cmdline_ptr = (unsigned long)cmdline_ptr;
break;
--
2.25.1
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-06-26 10:38 [PATCH] LoongArch: kexec: Fix address space mismatch in command line lookup George Guo
2026-06-26 10:51 George Guo
2026-06-30 8:25 ` Huacai Chen
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