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Date: Tue, 17 Dec 2019 13:45:28 -0600
From: Tianlin Li <tli@...italocean.com>
To: kernel-hardening@...ts.openwall.com,
	keescook@...omium.org
Cc: Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	Tianlin Li <tli@...italocean.com>
Subject: [PATCH] drivers/misc: have the callers of set_memory_*() check the return value

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@...italocean.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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