arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0

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.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210730112443.23245-12-will@kernel.org

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dc..97932fb 100644 (file)
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -213,10 +213,8 @@ typedef compat_elf_greg_t          compat_elf_gregset_t[COMPAT_ELF_NGREG];
 
 /* AArch32 EABI. */
 #define EF_ARM_EABI_MASK               0xff000000
-#define compat_elf_check_arch(x)       (system_supports_32bit_el0() && \
-                                        ((x)->e_machine == EM_ARM) && \
-                                        ((x)->e_flags & EF_ARM_EABI_MASK))
-
+int compat_elf_check_arch(const struct elf32_hdr *);
+#define compat_elf_check_arch          compat_elf_check_arch
 #define compat_start_thread            compat_start_thread
 /*
  * Unlike the native SET_PERSONALITY macro, the compat version maintains

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index c8989b9..583ee58 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -21,6 +21,7 @@
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/nospec.h>
+#include <linux/sched.h>
 #include <linux/stddef.h>
 #include <linux/sysctl.h>
 #include <linux/unistd.h>
@@ -579,6 +580,28 @@ unsigned long arch_align_stack(unsigned long sp)
        return sp & ~0xf;
 }
 
+#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) ||
+              !dl_task_check_affinity(current, system_32bit_el0_cpumask());
+}
+#endif
+
 /*
  * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
  */
@@ -588,8 +611,22 @@ void arch_setup_new_exec(void)
 
        if (is_compat_task()) {
                mmflags = MMCF_AARCH32;
-               if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
+
+               /*
+                * Restrict the CPU affinity mask for a 32-bit task so that
+                * it contains only 32-bit-capable CPUs.
+                *
+                * From the perspective of the task, this looks similar to
+                * what would happen if the 64-bit-only CPUs were hot-unplugged
+                * at the point of execve(), although we try a bit harder to
+                * honour the cpuset hierarchy.
+                */
+               if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+                       force_compatible_cpus_allowed_ptr(current);
                        set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+               }
+       } else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+               relax_compatible_cpus_allowed_ptr(current);
        }
 
        current->mm->context.flags = mmflags;