Signal frames do not have a fixed format and can vary in size when a number of things change: support XSAVE features, 32 vs. 64-bit apps. Add the code to support 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. Locate the body of the helper function -- fpu__get_fpstate_sigframe_size() in fpu/signal.c for its relevance. Signed-off-by: Chang S. Bae <[email protected]> Reviewed-by: Len Brown <[email protected]> Acked-by: H.J. Lu <[email protected]> Cc: [email protected] Cc: [email protected] --- Change from v1: * Took stack alignment into account for sigframe size (Dave Martin) --- arch/x86/include/asm/fpu/signal.h | 2 + arch/x86/include/asm/sigframe.h | 23 ++++++++++++ arch/x86/kernel/cpu/common.c | 3 ++ arch/x86/kernel/fpu/signal.c | 20 ++++++++++ arch/x86/kernel/signal.c | 61 ++++++++++++++++++++++++++++++- 5 files changed, 107 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h index 7fb516b6893a..5bfbf8f2e5a3 100644 --- a/arch/x86/include/asm/fpu/signal.h +++ b/arch/x86/include/asm/fpu/signal.h @@ -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_sigframe_size(void); + extern void fpu__init_prepare_fx_sw_frame(void); #endif /* _ASM_X86_FPU_SIGNAL_H */ diff --git a/arch/x86/include/asm/sigframe.h b/arch/x86/include/asm/sigframe.h index 84eab2724875..ac77f3f90bc9 100644 --- a/arch/x86/include/asm/sigframe.h +++ b/arch/x86/include/asm/sigframe.h @@ -52,6 +52,15 @@ struct rt_sigframe_ia32 { char retcode[8]; /* fp state follows here */ }; + +#define SIZEOF_sigframe_ia32 sizeof(struct sigframe_ia32) +#define SIZEOF_rt_sigframe_ia32 sizeof(struct rt_sigframe_ia32) + +#else + +#define SIZEOF_sigframe_ia32 0 +#define SIZEOF_rt_sigframe_ia32 0 + #endif /* defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) */ #ifdef CONFIG_X86_64 @@ -81,8 +90,22 @@ struct rt_sigframe_x32 { /* fp state follows here */ }; +#define SIZEOF_rt_sigframe_x32 sizeof(struct rt_sigframe_x32) + #endif /* CONFIG_X86_X32_ABI */ +#define SIZEOF_rt_sigframe sizeof(struct rt_sigframe) + +#else + +#define SIZEOF_rt_sigframe 0 + #endif /* CONFIG_X86_64 */ +#ifndef SIZEOF_rt_sigframe_x32 +#define SIZEOF_rt_sigframe_x32 0 +#endif + +void __init init_sigframe_size(void); + #endif /* _ASM_X86_SIGFRAME_H */ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 35ad8480c464..6954932272d5 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -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" @@ -1331,6 +1332,8 @@ 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 diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index a4ec65317a7f..9f009525f551 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -507,6 +507,26 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame, return sp; } + +unsigned long fpu__get_fpstate_sigframe_size(void) +{ + unsigned long xstate_size = xstate_sigframe_size(); + unsigned long fsave_header_size = 0; + + /* + * 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()) + fsave_header_size = sizeof(struct fregs_state); + + return fsave_header_size + xstate_size; +} + /* * Prepare the SW reserved portion of the fxsave memory layout, indicating * the presence of the extended state information in the memory layout diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index be0d7d4152ec..bae35ff6e744 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -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 +668,58 @@ SYSCALL_DEFINE0(rt_sigreturn) return 0; } +/* + * 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) +{ + /* + * Use the largest of possible structure formats. This might + * slightly oversize the frame for 64-bit apps. + */ + + if (IS_ENABLED(CONFIG_X86_32) || + IS_ENABLED(CONFIG_IA32_EMULATION)) + max_frame_size = max((unsigned long)SIZEOF_sigframe_ia32, + (unsigned long)SIZEOF_rt_sigframe_ia32); + + if (IS_ENABLED(CONFIG_X86_X32_ABI)) + max_frame_size = max(max_frame_size, (unsigned long)SIZEOF_rt_sigframe_x32); + + if (IS_ENABLED(CONFIG_X86_64)) + max_frame_size = max(max_frame_size, (unsigned long)SIZEOF_rt_sigframe); + + max_frame_size += MAX_FRAME_PADDING; + + max_frame_size += fpu__get_fpstate_sigframe_size() + MAX_XSAVE_PADDING; + + /* Userspace expects an aligned size. */ + max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT); +} + static inline int is_ia32_compat_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_IA32_EMULATION) && -- 2.17.1
