From: Alexey Dobriyan <adobriyan@gmail.com>
To: Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Florian Weimer <fweimer@redhat.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, x86@kernel.org,
Eric Biederman <ebiederm@xmission.com>,
linux-mm@kvack.org
Subject: [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts
Date: Mon, 5 Feb 2024 12:51:43 +0300 [thread overview]
Message-ID: <ecb049aa-bcac-45c7-bbb1-4612d094935a@p183> (raw)
Report available page shifts in arch independent manner, so that
userspace developers won't have to parse /proc/cpuinfo hunting
for arch specific strings.
Main users are supposed to be libhugetlbfs-like libraries which try
to abstract huge mappings across multiple architectures. Regular code
which queries hugepage support before using them benefits too because
it doesn't have to deal with descriptors and parsing sysfs hierarchies
while enjoying the simplicity and speed of getauxval(3).
Note 1!
This is strictly for userspace, if some page size is shutdown due
to kernel command line option or CPU bug workaround, than it must
not be reported in aux vector!
Note 2!
getauxval(AT_PAGE_SHIFT_MASK) output is a function of CPU capabilities
only, it is not changed by system memory size, hugepage availability at
any given moment, hugetlbfs being mounted, etc.
Example output:
x86_64 machine with 1 GiB pages:
00000030 06 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00
00000040 1d 00 00 00 00 00 00 00 00 10 20 40 00 00 00 00
x86_64 machine with 2 MiB pages only:
00000030 06 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00
00000040 1d 00 00 00 00 00 00 00 00 10 20 00 00 00 00 00
AT_PAGESZ always reports one smallest page size which is not interesting.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
changes since v3 -- even better changelog
arch/x86/include/asm/elf.h | 12 ++++++++++++
fs/binfmt_elf.c | 3 +++
include/uapi/linux/auxvec.h | 13 +++++++++++++
3 files changed, 28 insertions(+)
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -358,6 +358,18 @@ else if (IS_ENABLED(CONFIG_IA32_EMULATION)) \
#define COMPAT_ELF_ET_DYN_BASE (TASK_UNMAPPED_BASE + 0x1000000)
+#define ARCH_AT_PAGE_SHIFT_MASK \
+ do { \
+ u32 val = 1 << 12; \
+ if (boot_cpu_has(X86_FEATURE_PSE)) { \
+ val |= 1 << 21; \
+ } \
+ if (boot_cpu_has(X86_FEATURE_GBPAGES)) { \
+ val |= 1 << 30; \
+ } \
+ NEW_AUX_ENT(AT_PAGE_SHIFT_MASK, val); \
+ } while (0)
+
#endif /* !CONFIG_X86_32 */
#define VDSO_CURRENT_BASE ((unsigned long)current->mm->context.vdso)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -240,6 +240,9 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
#endif
NEW_AUX_ENT(AT_HWCAP, ELF_HWCAP);
NEW_AUX_ENT(AT_PAGESZ, ELF_EXEC_PAGESIZE);
+#ifdef ARCH_AT_PAGE_SHIFT_MASK
+ ARCH_AT_PAGE_SHIFT_MASK;
+#endif
NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC);
NEW_AUX_ENT(AT_PHDR, phdr_addr);
NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
--- a/include/uapi/linux/auxvec.h
+++ b/include/uapi/linux/auxvec.h
@@ -33,6 +33,19 @@
#define AT_RSEQ_FEATURE_SIZE 27 /* rseq supported feature size */
#define AT_RSEQ_ALIGN 28 /* rseq allocation alignment */
+/*
+ * All page sizes supported by CPU encoded as bitmask.
+ *
+ * Example: x86_64 system with pse, pdpe1gb /proc/cpuinfo flags
+ * reports 4 KiB, 2 MiB and 1 GiB page support.
+ *
+ * $ LD_SHOW_AUXV=1 $(which true) | grep -e AT_PAGE_SHIFT_MASK
+ * AT_PAGE_SHIFT_MASK: 0x40201000
+ *
+ * For 2^64 hugepage support please contact your Universe sales representative.
+ */
+#define AT_PAGE_SHIFT_MASK 29
+
#define AT_EXECFN 31 /* filename of program */
#ifndef AT_MINSIGSTKSZ
next reply other threads:[~2024-02-05 9:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-05 9:51 Alexey Dobriyan [this message]
2024-02-05 12:48 ` [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts Kees Cook
2024-02-09 12:30 ` Alexey Dobriyan
2024-02-10 0:41 ` Kees Cook
2024-02-13 18:51 ` Alexey Dobriyan
2024-02-13 19:39 ` Kees Cook
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ecb049aa-bcac-45c7-bbb1-4612d094935a@p183 \
--to=adobriyan@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=ebiederm@xmission.com \
--cc=fweimer@redhat.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mingo@redhat.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).