net_if: misaligned access

Describe the bug
UB sanitizers finds misaligned reads/writes of struct in_addr when running in native_sim.

To Reproduce

1. Build for native_sim with UB-sanitizer enabled
2. Run the sim
3. Network Ping
4. ->UB sanitizer finds misaligned accesses

Expected behavior
UB sanitizer should not find misaligned access under those circumstances.

Impact

• Either those are a real problem
• Or they are false positives, and the UB sanitizer can not be used to test an application in above circumstances to find actual problems

Logs and console output
Snippes tripping UBsan:

/**
 * @brief Check if the IPv4 address is a loopback address (127.0.0.0/8).
 *
 * @param addr IPv4 address
 *
 * @return True if address is a loopback address, False otherwise.
 */
static inline bool net_ipv4_is_addr_loopback(struct in_addr *addr)
{
	return addr->s4_addr[0] == 127U;
}

/**
 *  @brief Compare two IPv4 addresses
 *
 *  @param addr1 Pointer to IPv4 address.
 *  @param addr2 Pointer to IPv4 address.
 *
 *  @return True if the addresses are the same, false otherwise.
 */
static inline bool net_ipv4_addr_cmp(const struct in_addr *addr1,
				     const struct in_addr *addr2)
{
	return UNALIGNED_GET(&addr1->s_addr) == UNALIGNED_GET(&addr2->s_addr);
}

/**
 * @brief Check if the IPv4 address is a multicast address.
 *
 * @param addr IPv4 address
 *
 * @return True if address is multicast address, False otherwise.
 */
static inline bool net_ipv4_is_addr_mcast(const struct in_addr *addr)
{
	return (ntohl(UNALIGNED_GET(&addr->s_addr)) & 0xF0000000) == 0xE0000000;
}

Environment (please complete the following information):
TBD

Additional context
TBD

[tpambor]

These are false-positive, as UNALIGNED_GET can be optimized away on architectures that allow unaligned memory access. UBSan does not see that we are aware of the potential unaligned access by using the UNALIGNED_GET macro. It only sees that we want to dereference a struct element with unaligned access. To solve this, UBSan alignment checks should be suppressed for accesses with the UNALIGNED_GET macro by using __attribute__((no_sanitize("alignment"))).

[jukkar]

There was issues before we added UNALIGNED_GET() calls, But these were fixed many years go.

[tpambor]

A reproducing example can be found here: https://godbolt.org/z/nvf9dGGYM

Cortex-M0 does not support unaligned memory accesses. The function test_no_unaligned_get demonstrates that without UNALIGNED_GET the compiler generates a normal 32-bit memory access which would cause a fault for unaligned addresses.

In comparison, test_unaligned_get_broken correctly generates multiple 8-bit accesses to avoid unaligned memory accesses, but UBSan would trap if the passed address is unaligned, although the code would execute correctly.

test_unaligned_get_safe is marked with __attribute__((no_sanitize("alignment"))) and UBSan does not generate traps here for unaligned accesses.

[jukkar]

Closing as there is no issue here.

Closing as there is no issue here.

Agree, that it is a false triggering of the UBsan. But it would be helpful to avoid the false positive. Would it be ok to add this __attribute__((no_sanitize("alignment"))) to the respective function?

[jukkar]

Perhaps the unaligned macro could be modified to have the extra attribute?

Perhaps the unaligned macro could be modified to have the extra attribute?

That would be great.
I can try if it would be fixed.