Commit 939ef713 authored by Chang S. Bae's avatar Chang S. Bae Committed by Borislav Petkov
Browse files

x86/signal: Introduce helpers to get the maximum signal frame size 



Signal frames do not have a fixed format and can vary in size when a number
of things change: supported XSAVE features, 32 vs. 64-bit apps, etc.

Add support for a runtime method for userspace to dynamically discover
how large a signal stack needs to be.

Introduce a new variable, max_frame_size, and helper functions for the
calculation to be used in a new user interface. Set max_frame_size to a
system-wide worst-case value, instead of storing multiple app-specific
values.

Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarLen Brown <len.brown@intel.com>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarH.J. Lu <hjl.tools@gmail.com>
Link: https://lkml.kernel.org/r/20210518200320.17239-3-chang.seok.bae@intel.com
parent 7cd60e43

arch/x86/include/asm/fpu/signal.h

+2 −0
Original line number Diff line number Diff line
@@ -29,6 +29,8 @@ unsigned long 
fpu__alloc_mathframe(unsigned long sp, int ia32_frame,

		     unsigned long *buf_fx, unsigned long *size);



unsigned long fpu__get_fpstate_size(void);



extern void fpu__init_prepare_fx_sw_frame(void);



#endif /* _ASM_X86_FPU_SIGNAL_H */

arch/x86/include/asm/sigframe.h

+2 −0
Original line number Diff line number Diff line
@@ -85,4 +85,6 @@ struct rt_sigframe_x32 { 


#endif /* CONFIG_X86_64 */



void __init init_sigframe_size(void);



#endif /* _ASM_X86_SIGFRAME_H */

arch/x86/kernel/cpu/common.c

+3 −0
Original line number Diff line number Diff line
@@ -58,6 +58,7 @@ 
#include <asm/intel-family.h>

#include <asm/cpu_device_id.h>

#include <asm/uv/uv.h>

#include <asm/sigframe.h>



#include "cpu.h"
@@ -1332,6 +1333,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) 


	fpu__init_system(c);



	init_sigframe_size();



#ifdef CONFIG_X86_32

	/*

	 * Regardless of whether PCID is enumerated, the SDM says

arch/x86/kernel/fpu/signal.c

+19 −0
Original line number Diff line number Diff line
@@ -507,6 +507,25 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame, 


	return sp;

}



unsigned long fpu__get_fpstate_size(void)

{

	unsigned long ret = xstate_sigframe_size();



	/*

	 * This space is needed on (most) 32-bit kernels, or when a 32-bit

	 * app is running on a 64-bit kernel. To keep things simple, just

	 * assume the worst case and always include space for 'freg_state',

	 * even for 64-bit apps on 64-bit kernels. This wastes a bit of

	 * space, but keeps the code simple.

	 */

	if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||

	     IS_ENABLED(CONFIG_X86_32)) && use_fxsr())

		ret += sizeof(struct fregs_state);



	return ret;

}



/*

 * Prepare the SW reserved portion of the fxsave memory layout, indicating

 * the presence of the extended state information in the memory layout

arch/x86/kernel/signal.c

+57 −2
Original line number Diff line number Diff line
@@ -212,6 +212,11 @@ do { \ 
 * Set up a signal frame.

 */



/* x86 ABI requires 16-byte alignment */

#define FRAME_ALIGNMENT	16UL



#define MAX_FRAME_PADDING	(FRAME_ALIGNMENT - 1)



/*

 * Determine which stack to use..

 */
@@ -222,9 +227,9 @@ static unsigned long align_sigframe(unsigned long sp) 
	 * Align the stack pointer according to the i386 ABI,

	 * i.e. so that on function entry ((sp + 4) & 15) == 0.

	 */

	sp = ((sp + 4) & -16ul) - 4;

	sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4;

#else /* !CONFIG_X86_32 */

	sp = round_down(sp, 16) - 8;

	sp = round_down(sp, FRAME_ALIGNMENT) - 8;

#endif

	return sp;

}
@@ -663,6 +668,56 @@ SYSCALL_DEFINE0(rt_sigreturn) 
	return 0;

}



/*

 * There are four different struct types for signal frame: sigframe_ia32,

 * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case

 * -- the largest size. It means the size for 64-bit apps is a bit more

 * than needed, but this keeps the code simple.

 */

#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)

# define MAX_FRAME_SIGINFO_UCTXT_SIZE	sizeof(struct sigframe_ia32)

#else

# define MAX_FRAME_SIGINFO_UCTXT_SIZE	sizeof(struct rt_sigframe)

#endif



/*

 * The FP state frame contains an XSAVE buffer which must be 64-byte aligned.

 * If a signal frame starts at an unaligned address, extra space is required.

 * This is the max alignment padding, conservatively.

 */

#define MAX_XSAVE_PADDING	63UL



/*

 * The frame data is composed of the following areas and laid out as:

 *

 * -------------------------

 * | alignment padding     |

 * -------------------------

 * | (f)xsave frame        |

 * -------------------------

 * | fsave header          |

 * -------------------------

 * | alignment padding     |

 * -------------------------

 * | siginfo + ucontext    |

 * -------------------------

 */



/* max_frame_size tells userspace the worst case signal stack size. */

static unsigned long __ro_after_init max_frame_size;



void __init init_sigframe_size(void)

{

	max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING;



	max_frame_size += fpu__get_fpstate_size() + MAX_XSAVE_PADDING;



	/* Userspace expects an aligned size. */

	max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT);



	pr_info("max sigframe size: %lu\n", max_frame_size);

}



static inline int is_ia32_compat_frame(struct ksignal *ksig)

{

	return IS_ENABLED(CONFIG_IA32_EMULATION) &&