Turn thread.fpu into a pointer. Since most FPU code internals work by passing
around the FPU pointer already, the code generation impact is small.
This allows us to remove the old kludge of task_struct being variable size:
struct task_struct {
...
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
*/
randomized_struct_fields_end
/* CPU-specific state of this task: */
struct thread_struct thread;
/*
* WARNING: on x86, 'thread_struct' contains a variable-sized
* structure. It *MUST* be at the end of 'task_struct'.
*
* Do not put anything below here!
*/
};
... which creates a number of problems, such as requiring thread_struct to be
the last member of the struct - not allowing it to be struct-randomized, etc.
But the primary motivation is to allow the decoupling of task_struct from
hardware details (<asm/processor.h> in particular), and to eventually allow
the per-task infrastructure:
DECLARE_PER_TASK(type, name);
...
per_task(current, name) = val;
... which requires task_struct to be a constant size struct.
The fpu_thread_struct_whitelist() quirk to hardened usercopy can be removed,
now that the FPU structure is not embedded in the task struct anymore, which
reduces text footprint a bit.
Fixed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-4-mingo@kernel.org
#endif
/* Floating point and extended processor state */
- struct fpu fpu;
- /*
- * WARNING: 'fpu' is dynamically-sized. It *MUST* be at
- * the end.
- */
+ struct fpu *fpu;
};
-#define x86_task_fpu(task) (&(task)->thread.fpu)
-
-extern void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size);
+#define x86_task_fpu(task) ((task)->thread.fpu)
-static inline void arch_thread_struct_whitelist(unsigned long *offset,
- unsigned long *size)
+/*
+ * X86 doesn't need any embedded-FPU-struct quirks:
+ */
+static inline void
+arch_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
{
- fpu_thread_struct_whitelist(offset, size);
+ *offset = 0;
+ *size = 0;
}
static inline void
int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
unsigned long ssp)
{
+ /*
+ * We allocate the new FPU structure right after the end of the task struct.
+ * task allocation size already took this into account.
+ *
+ * This is safe because task_struct size is a multiple of cacheline size.
+ */
struct fpu *src_fpu = x86_task_fpu(current);
- struct fpu *dst_fpu = x86_task_fpu(dst);
+ struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
+
+ BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
+ BUG_ON(!src_fpu);
+
+ dst->thread.fpu = dst_fpu;
/* The new task's FPU state cannot be valid in the hardware. */
dst_fpu->last_cpu = -1;
return 0;
}
-/*
- * Whitelist the FPU register state embedded into task_struct for hardened
- * usercopy.
- */
-void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
-{
- *offset = offsetof(struct thread_struct, fpu.__fpstate.regs);
- *size = fpu_kernel_cfg.default_size;
-}
-
/*
* Drops current FPU state: deactivates the fpregs and
* the fpstate. NOTE: it still leaves previous contents
return fsw == 0 && (fcw & 0x103f) == 0x003f;
}
+static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
+
static void __init fpu__init_system_early_generic(void)
{
+ fpstate_reset(&x86_init_fpu);
+ current->thread.fpu = &x86_init_fpu;
+ set_thread_flag(TIF_NEED_FPU_LOAD);
+ x86_init_fpu.last_cpu = -1;
+
if (!boot_cpu_has(X86_FEATURE_CPUID) &&
!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
if (fpu__probe_without_cpuid())
{
int task_size = sizeof(struct task_struct);
+ task_size += sizeof(struct fpu);
+
/*
* Subtract off the static size of the register state.
* It potentially has a bunch of padding.
/*
* We dynamically size 'struct fpu', so we require that
- * it be at the end of 'thread_struct' and that
- * 'thread_struct' be at the end of 'task_struct'. If
- * you hit a compile error here, check the structure to
- * see if something got added to the end.
+ * 'state' be at the end of 'it:
*/
CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
- CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
- CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
arch_task_struct_size = task_size;
}
*/
void __init fpu__init_system(void)
{
- fpstate_reset(x86_task_fpu(current));
fpu__init_system_early_generic();
/*
dst->thread.vm86 = NULL;
#endif
/* Drop the copied pointer to current's fpstate */
- x86_task_fpu(dst)->fpstate = NULL;
+ dst->thread.fpu = NULL;
return 0;
}
struct user_event_mm *user_event_mm;
#endif
- /*
- * New fields for task_struct should be added above here, so that
- * they are included in the randomized portion of task_struct.
- */
- randomized_struct_fields_end
-
/* CPU-specific state of this task: */
struct thread_struct thread;
/*
- * WARNING: on x86, 'thread_struct' contains a variable-sized
- * structure. It *MUST* be at the end of 'task_struct'.
- *
- * Do not put anything below here!
+ * New fields for task_struct should be added above here, so that
+ * they are included in the randomized portion of task_struct.
*/
-};
+ randomized_struct_fields_end
+} __attribute__ ((aligned (64)));
#define TASK_REPORT_IDLE (TASK_REPORT + 1)
#define TASK_REPORT_MAX (TASK_REPORT_IDLE << 1)
projects / linux.git / commitdiff