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Subject[PATCH] drivers/misc: have the callers of set_memory_*() check the return value
Date
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
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