[PATCH 30/82] s390/kexec_file: Refactor intentional wrap-around calculation

[PATCH 30/82] s390/kexec_file: Refactor intentional wrap-around calculation

[Kees Cook]

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded unsigned wrap-around addition test to use
check_add_overflow(), retaining the result for later usage (which removes
the redundant open-coded addition). This paves the way to enabling the
unsigned wrap-around sanitizer[2] in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Nico Boehr <nrb@linux.ibm.com>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Tao Liu <ltao@redhat.com>
Cc: Alexander Egorenkov <egorenar@linux.ibm.com>
Cc: linux-s390@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/s390/include/asm/stacktrace.h    | 6 ++++--
 arch/s390/kernel/machine_kexec_file.c | 5 +++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
index 31ec4f545e03..3ce08d32a8ad 100644
--- a/arch/s390/include/asm/stacktrace.h
+++ b/arch/s390/include/asm/stacktrace.h
@@ -34,11 +34,13 @@ int get_stack_info(unsigned long sp, struct task_struct *task,
 static inline bool on_stack(struct stack_info *info,
 			    unsigned long addr, size_t len)
 {
+	unsigned long sum;
+
 	if (info->type == STACK_TYPE_UNKNOWN)
 		return false;
-	if (addr + len < addr)
+	if (check_add_overflow(addr, len, &sum))
 		return false;
-	return addr >= info->begin && addr + len <= info->end;
+	return addr >= info->begin && sum <= info->end;
 }
 
 /*
diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
index 8d207b82d9fe..e5e925423061 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -238,6 +238,7 @@ void *kexec_file_add_components(struct kimage *image,
 	unsigned long max_command_line_size = LEGACY_COMMAND_LINE_SIZE;
 	struct s390_load_data data = {0};
 	unsigned long minsize;
+	unsigned long sum;
 	int ret;
 
 	data.report = ipl_report_init(&ipl_block);
@@ -256,10 +257,10 @@ void *kexec_file_add_components(struct kimage *image,
 	if (data.parm->max_command_line_size)
 		max_command_line_size = data.parm->max_command_line_size;
 
-	if (minsize + max_command_line_size < minsize)
+	if (check_add_overflow(minsize, max_command_line_size, &sum))
 		goto out;
 
-	if (image->kernel_buf_len < minsize + max_command_line_size)
+	if (image->kernel_buf_len < sum)
 		goto out;
 
 	if (image->cmdline_buf_len >= max_command_line_size)
-- 
2.34.1

[PATCH 58/82] s390/mm: Refactor intentional wrap-around test

[Kees Cook]

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/s390/mm/gmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 6f96b5a71c63..977b61ab59f2 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -411,7 +411,7 @@ int gmap_unmap_segment(struct gmap *gmap, unsigned long to, unsigned long len)
 	BUG_ON(gmap_is_shadow(gmap));
 	if ((to | len) & (PMD_SIZE - 1))
 		return -EINVAL;
-	if (len == 0 || to + len < to)
+	if (len == 0 || add_would_overflow(to, len))
 		return -EINVAL;
 
 	flush = 0;
@@ -443,7 +443,7 @@ int gmap_map_segment(struct gmap *gmap, unsigned long from,
 	BUG_ON(gmap_is_shadow(gmap));
 	if ((from | to | len) & (PMD_SIZE - 1))
 		return -EINVAL;
-	if (len == 0 || from + len < from || to + len < to ||
+	if (len == 0 || add_would_overflow(from, len) || add_would_overflow(to, len) ||
 	    from + len - 1 > TASK_SIZE_MAX || to + len - 1 > gmap->asce_end)
 		return -EINVAL;
 
-- 
2.34.1

[PATCH 71/82] s390/mm: Refactor intentional wrap-around test

[Kees Cook]

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: linux-s390@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/s390/mm/vmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 186a020857cf..98a7f08141f0 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -538,7 +538,7 @@ int vmem_add_mapping(unsigned long start, unsigned long size)
 
 	if (start < range.start ||
 	    start + size > range.end + 1 ||
-	    start + size < start)
+	    add_would_overflow(start, size))
 		return -ERANGE;
 
 	mutex_lock(&vmem_mutex);
-- 
2.34.1

Re: [PATCH 30/82] s390/kexec_file: Refactor intentional wrap-around calculation

[Alexander Gordeev]

On Mon, Jan 22, 2024 at 04:27:05PM -0800, Kees Cook wrote:

Hi Kees,

...
>  arch/s390/include/asm/stacktrace.h    | 6 ++++--
>  arch/s390/kernel/machine_kexec_file.c | 5 +++--

Subject does not match. These need to be two separate commits.

>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
> index 31ec4f545e03..3ce08d32a8ad 100644
> --- a/arch/s390/include/asm/stacktrace.h
> +++ b/arch/s390/include/asm/stacktrace.h
> @@ -34,11 +34,13 @@ int get_stack_info(unsigned long sp, struct task_struct *task,
>  static inline bool on_stack(struct stack_info *info,
>  			    unsigned long addr, size_t len)
>  {
> +	unsigned long sum;
> +
>  	if (info->type == STACK_TYPE_UNKNOWN)
>  		return false;
> -	if (addr + len < addr)
> +	if (check_add_overflow(addr, len, &sum))

Why not add_would_overflow()?

>  		return false;
> -	return addr >= info->begin && addr + len <= info->end;
> +	return addr >= info->begin && sum <= info->end;
>  }
>  
>  /*
> diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
> index 8d207b82d9fe..e5e925423061 100644
> --- a/arch/s390/kernel/machine_kexec_file.c
> +++ b/arch/s390/kernel/machine_kexec_file.c
> @@ -238,6 +238,7 @@ void *kexec_file_add_components(struct kimage *image,
>  	unsigned long max_command_line_size = LEGACY_COMMAND_LINE_SIZE;
>  	struct s390_load_data data = {0};
>  	unsigned long minsize;
> +	unsigned long sum;

Please, use min_kernel_buf_len instead of sum.

@Sven, could you please correct me if (minsize + max_command_line_size)
means something else.

>  	int ret;
>  
>  	data.report = ipl_report_init(&ipl_block);
> @@ -256,10 +257,10 @@ void *kexec_file_add_components(struct kimage *image,
>  	if (data.parm->max_command_line_size)
>  		max_command_line_size = data.parm->max_command_line_size;
>  
> -	if (minsize + max_command_line_size < minsize)
> +	if (check_add_overflow(minsize, max_command_line_size, &sum))
>  		goto out;
>  
> -	if (image->kernel_buf_len < minsize + max_command_line_size)
> +	if (image->kernel_buf_len < sum)
>  		goto out;
>  
>  	if (image->cmdline_buf_len >= max_command_line_size)

Thanks!

Re: [PATCH 30/82] s390/kexec_file: Refactor intentional wrap-around calculation

[Sven Schnelle]

Alexander Gordeev <agordeev@linux.ibm.com> writes:

> On Mon, Jan 22, 2024 at 04:27:05PM -0800, Kees Cook wrote:
>> diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
>> index 8d207b82d9fe..e5e925423061 100644
>> --- a/arch/s390/kernel/machine_kexec_file.c
>> +++ b/arch/s390/kernel/machine_kexec_file.c
>> @@ -238,6 +238,7 @@ void *kexec_file_add_components(struct kimage *image,
>>  	unsigned long max_command_line_size = LEGACY_COMMAND_LINE_SIZE;
>>  	struct s390_load_data data = {0};
>>  	unsigned long minsize;
>> +	unsigned long sum;
>
> Please, use min_kernel_buf_len instead of sum.
>
> @Sven, could you please correct me if (minsize + max_command_line_size)
> means something else.

Your understanding is correct, minsize + max_command_line_size is the
minimum required size of the kernel image.