Re: [PATCH v8 14/19] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0

On 6/2/21 6:47 PM, Will Deacon wrote:

When exec'ing a 32-bit task on a system with mismatched support for
32-bit EL0, try to ensure that it starts life on a CPU that can actually
run it.

Similarly, when exec'ing a 64-bit task on such a system, try to restore
the old affinity mask if it was previously restricted.

Reviewed-by: Quentin Perret <redacted>
Signed-off-by: Will Deacon <will@kernel.org>
---

[...]

 
+#ifdef CONFIG_COMPAT
+int compat_elf_check_arch(const struct elf32_hdr *hdr)
+{
+	if (!system_supports_32bit_el0())
+		return false;
+
+	if ((hdr)->e_machine != EM_ARM)
+		return false;
+
+	if (!((hdr)->e_flags & EF_ARM_EABI_MASK))
+		return false;
+
+	/*
+	 * Prevent execve() of a 32-bit program from a deadline task
+	 * if the restricted affinity mask would be inadmissible on an
+	 * asymmetric system.
+	 */
+	return !static_branch_unlikely(&arm64_mismatched_32bit_el0) ||
+	       task_cpus_dl_admissible(current, system_32bit_el0_cpumask());
+}
+#endif

From the DL perspective:

Reviewed-by: Daniel Bristot de Oliveira <redacted>

Thanks!
-- Daniel


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