diff options
| -rw-r--r-- | Documentation/x86/elf_auxvec.rst | 53 | ||||
| -rw-r--r-- | Documentation/x86/index.rst | 1 | ||||
| -rw-r--r-- | arch/x86/include/asm/elf.h | 4 | ||||
| -rw-r--r-- | arch/x86/include/uapi/asm/auxvec.h | 4 | ||||
| -rw-r--r-- | arch/x86/kernel/signal.c | 5 |
5 files changed, 65 insertions, 2 deletions
diff --git a/Documentation/x86/elf_auxvec.rst b/Documentation/x86/elf_auxvec.rst new file mode 100644 index 000000000000..18e4744717f9 --- /dev/null +++ b/Documentation/x86/elf_auxvec.rst @@ -0,0 +1,53 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================== +x86-specific ELF Auxiliary Vectors +================================== + +This document describes the semantics of the x86 auxiliary vectors. + +Introduction +============ + +ELF Auxiliary vectors enable the kernel to efficiently provide +configuration-specific parameters to userspace. In this example, a program +allocates an alternate stack based on the kernel-provided size:: + + #include <sys/auxv.h> + #include <elf.h> + #include <signal.h> + #include <stdlib.h> + #include <assert.h> + #include <err.h> + + #ifndef AT_MINSIGSTKSZ + #define AT_MINSIGSTKSZ 51 + #endif + + .... + stack_t ss; + + ss.ss_sp = malloc(ss.ss_size); + assert(ss.ss_sp); + + ss.ss_size = getauxval(AT_MINSIGSTKSZ) + SIGSTKSZ; + ss.ss_flags = 0; + + if (sigaltstack(&ss, NULL)) + err(1, "sigaltstack"); + + +The exposed auxiliary vectors +============================= + +AT_SYSINFO is used for locating the vsyscall entry point. It is not +exported on 64-bit mode. + +AT_SYSINFO_EHDR is the start address of the page containing the vDSO. + +AT_MINSIGSTKSZ denotes the minimum stack size required by the kernel to +deliver a signal to user-space. AT_MINSIGSTKSZ comprehends the space +consumed by the kernel to accommodate the user context for the current +hardware configuration. It does not comprehend subsequent user-space stack +consumption, which must be added by the user. (e.g. Above, user-space adds +SIGSTKSZ to AT_MINSIGSTKSZ.) diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 4693e192b447..d58614d5cde6 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -35,3 +35,4 @@ x86-specific Documentation sva sgx features + elf_auxvec diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 7d7500806af8..29fea180a665 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -312,6 +312,7 @@ do { \ NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \ NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \ } \ + NEW_AUX_ENT(AT_MINSIGSTKSZ, get_sigframe_size()); \ } while (0) /* @@ -328,6 +329,7 @@ extern unsigned long task_size_32bit(void); extern unsigned long task_size_64bit(int full_addr_space); extern unsigned long get_mmap_base(int is_legacy); extern bool mmap_address_hint_valid(unsigned long addr, unsigned long len); +extern unsigned long get_sigframe_size(void); #ifdef CONFIG_X86_32 @@ -349,6 +351,7 @@ do { \ if (vdso64_enabled) \ NEW_AUX_ENT(AT_SYSINFO_EHDR, \ (unsigned long __force)current->mm->context.vdso); \ + NEW_AUX_ENT(AT_MINSIGSTKSZ, get_sigframe_size()); \ } while (0) /* As a historical oddity, the x32 and x86_64 vDSOs are controlled together. */ @@ -357,6 +360,7 @@ do { \ if (vdso64_enabled) \ NEW_AUX_ENT(AT_SYSINFO_EHDR, \ (unsigned long __force)current->mm->context.vdso); \ + NEW_AUX_ENT(AT_MINSIGSTKSZ, get_sigframe_size()); \ } while (0) #define AT_SYSINFO 32 diff --git a/arch/x86/include/uapi/asm/auxvec.h b/arch/x86/include/uapi/asm/auxvec.h index 580e3c567046..6beb55bbefa4 100644 --- a/arch/x86/include/uapi/asm/auxvec.h +++ b/arch/x86/include/uapi/asm/auxvec.h @@ -12,9 +12,9 @@ /* entries in ARCH_DLINFO: */ #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64) -# define AT_VECTOR_SIZE_ARCH 2 +# define AT_VECTOR_SIZE_ARCH 3 #else /* else it's non-compat x86-64 */ -# define AT_VECTOR_SIZE_ARCH 1 +# define AT_VECTOR_SIZE_ARCH 2 #endif #endif /* _ASM_X86_AUXVEC_H */ diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 689a4b6dd18f..86e53868159a 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -718,6 +718,11 @@ void __init init_sigframe_size(void) pr_info("max sigframe size: %lu\n", max_frame_size); } +unsigned long get_sigframe_size(void) +{ + return max_frame_size; +} + static inline int is_ia32_compat_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_IA32_EMULATION) && |