* [PATCH] drivers/misc: have the callers of set_memory_*() check the return value
@ 2019-12-17 19:45 Tianlin Li
2019-12-17 23:57 ` Kees Cook
0 siblings, 1 reply; 2+ messages in thread
From: Tianlin Li @ 2019-12-17 19:45 UTC (permalink / raw)
To: kernel-hardening, keescook
Cc: Arnd Bergmann, Greg Kroah-Hartman, linux-kernel, Tianlin Li
Right now several architectures allow their set_memory_*() family of
functions to fail, but callers may not be checking the return values.
If set_memory_*() returns with an error, call-site assumptions may be
infact wrong to assume that it would either succeed or not succeed at
all. Ideally, the failure of set_memory_*() should be passed up the
call stack, and callers should examine the failure and deal with it.
Need to fix the callers and add the __must_check attribute. They also
may not provide any level of atomicity, in the sense that the memory
protections may be left incomplete on failure. This issue likely has a
few steps on effects architectures:
1)Have all callers of set_memory_*() helpers check the return value.
2)Add __must_check to all set_memory_*() helpers so that new uses do
not ignore the return value.
3)Add atomicity to the calls so that the memory protections aren't left
in a partial state.
This series is part of step 1. Make sram driver check the return value of
set_memory_*().
Signed-off-by: Tianlin Li <tli@digitalocean.com>
---
drivers/misc/sram-exec.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/misc/sram-exec.c b/drivers/misc/sram-exec.c
index d054e2842a5f..cb57ac6ab4c3 100644
--- a/drivers/misc/sram-exec.c
+++ b/drivers/misc/sram-exec.c
@@ -85,6 +85,7 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
unsigned long base;
int pages;
void *dst_cpy;
+ int ret;
mutex_lock(&exec_pool_list_mutex);
list_for_each_entry(p, &exec_pool_list, list) {
@@ -104,16 +105,28 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
mutex_lock(&part->lock);
- set_memory_nx((unsigned long)base, pages);
- set_memory_rw((unsigned long)base, pages);
+ ret = set_memory_nx((unsigned long)base, pages);
+ if (ret)
+ goto error_out;
+ ret = set_memory_rw((unsigned long)base, pages);
+ if (ret)
+ goto error_out;
dst_cpy = fncpy(dst, src, size);
- set_memory_ro((unsigned long)base, pages);
- set_memory_x((unsigned long)base, pages);
+ ret = set_memory_ro((unsigned long)base, pages);
+ if (ret)
+ goto error_out;
+ ret = set_memory_x((unsigned long)base, pages);
+ if (ret)
+ goto error_out;
mutex_unlock(&part->lock);
return dst_cpy;
+
+error_out:
+ mutex_unlock(&part->lock);
+ return NULL;
}
EXPORT_SYMBOL_GPL(sram_exec_copy);
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] drivers/misc: have the callers of set_memory_*() check the return value
2019-12-17 19:45 [PATCH] drivers/misc: have the callers of set_memory_*() check the return value Tianlin Li
@ 2019-12-17 23:57 ` Kees Cook
0 siblings, 0 replies; 2+ messages in thread
From: Kees Cook @ 2019-12-17 23:57 UTC (permalink / raw)
To: Tianlin Li
Cc: kernel-hardening, Arnd Bergmann, Greg Kroah-Hartman, linux-kernel
On Tue, Dec 17, 2019 at 01:45:28PM -0600, Tianlin Li wrote:
> Right now several architectures allow their set_memory_*() family of
> functions to fail, but callers may not be checking the return values.
> If set_memory_*() returns with an error, call-site assumptions may be
> infact wrong to assume that it would either succeed or not succeed at
> all. Ideally, the failure of set_memory_*() should be passed up the
> call stack, and callers should examine the failure and deal with it.
>
> Need to fix the callers and add the __must_check attribute. They also
> may not provide any level of atomicity, in the sense that the memory
> protections may be left incomplete on failure. This issue likely has a
> few steps on effects architectures:
> 1)Have all callers of set_memory_*() helpers check the return value.
> 2)Add __must_check to all set_memory_*() helpers so that new uses do
> not ignore the return value.
> 3)Add atomicity to the calls so that the memory protections aren't left
> in a partial state.
>
> This series is part of step 1. Make sram driver check the return value of
> set_memory_*().
>
> Signed-off-by: Tianlin Li <tli@digitalocean.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> drivers/misc/sram-exec.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/misc/sram-exec.c b/drivers/misc/sram-exec.c
> index d054e2842a5f..cb57ac6ab4c3 100644
> --- a/drivers/misc/sram-exec.c
> +++ b/drivers/misc/sram-exec.c
> @@ -85,6 +85,7 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
> unsigned long base;
> int pages;
> void *dst_cpy;
> + int ret;
>
> mutex_lock(&exec_pool_list_mutex);
> list_for_each_entry(p, &exec_pool_list, list) {
> @@ -104,16 +105,28 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
>
> mutex_lock(&part->lock);
>
> - set_memory_nx((unsigned long)base, pages);
> - set_memory_rw((unsigned long)base, pages);
> + ret = set_memory_nx((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
> + ret = set_memory_rw((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
>
> dst_cpy = fncpy(dst, src, size);
>
> - set_memory_ro((unsigned long)base, pages);
> - set_memory_x((unsigned long)base, pages);
> + ret = set_memory_ro((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
> + ret = set_memory_x((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
>
> mutex_unlock(&part->lock);
>
> return dst_cpy;
> +
> +error_out:
> + mutex_unlock(&part->lock);
> + return NULL;
> }
> EXPORT_SYMBOL_GPL(sram_exec_copy);
> --
> 2.17.1
>
--
Kees Cook
^ permalink raw reply [flat|nested] 2+ messages in thread
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