From ea41b029584d522ba0739511d1dd6ff070c90e1d Mon Sep 17 00:00:00 2001 From: "Chang S. Bae" Date: Tue, 18 May 2021 13:03:17 -0700 Subject: [PATCH] x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ mainline inclusion from mainline-v5.14-rc1 commit 1c33bb0507508af24fd754dd7123bd8e997fab2f category: feature bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I590ZC CVE: NA Intel-SIG: commit 1c33bb050750 x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ. -------------------------------- Historically, signal.h defines MINSIGSTKSZ (2KB) and SIGSTKSZ (8KB), for use by all architectures with sigaltstack(2). Over time, the hardware state size grew, but these constants did not evolve. Today, literal use of these constants on several architectures may result in signal stack overflow, and thus user data corruption. A few years ago, the ARM team addressed this issue by establishing getauxval(AT_MINSIGSTKSZ). This enables the kernel to supply a value at runtime that is an appropriate replacement on current and future hardware. Add getauxval(AT_MINSIGSTKSZ) support to x86, analogous to the support added for ARM in 94b07c1f8c39 ("arm64: signal: Report signal frame size to userspace via auxv"). Also, include a documentation to describe x86-specific auxiliary vectors. Signed-off-by: Chang S. Bae Signed-off-by: Borislav Petkov Reviewed-by: Len Brown Acked-by: Thomas Gleixner Link: https://lkml.kernel.org/r/20210518200320.17239-4-chang.seok.bae@intel.com Signed-off-by: Lin Wang --- Documentation/x86/elf_auxvec.rst | 53 ++++++++++++++++++++++++++++++ Documentation/x86/index.rst | 1 + arch/x86/include/asm/elf.h | 4 +++ arch/x86/include/uapi/asm/auxvec.h | 4 +-- arch/x86/kernel/signal.c | 5 +++ 5 files changed, 65 insertions(+), 2 deletions(-) create mode 100644 Documentation/x86/elf_auxvec.rst 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 + #include + #include + #include + #include + #include + + #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 6832df92f084..6b1384c13852 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -35,3 +35,4 @@ x86-specific Documentation x86_64/index sva sgx + elf_auxvec diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index d445bf8f5214..0876ba991601 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -314,6 +314,7 @@ 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) /* @@ -330,6 +331,7 @@ 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 @@ -351,6 +353,7 @@ 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. */ @@ -359,6 +362,7 @@ 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 04a76b28ee24..e941dc4c46bd 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -734,6 +734,11 @@ 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) && -- GitLab