From: Kees Cook <keescook@chromium.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>, Dave Martin <Dave.Martin@arm.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
x86-patch-review@intel.com
Subject: Re: [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support
Date: Tue, 25 Feb 2020 13:20:53 -0800 [thread overview]
Message-ID: <202002251319.030E727E99@keescook> (raw)
In-Reply-To: <20200205181935.3712-23-yu-cheng.yu@intel.com>
On Wed, Feb 05, 2020 at 10:19:30AM -0800, Yu-cheng Yu wrote:
> From: Dave Martin <Dave.Martin@arm.com>
>
> ELF program properties will be needed for detecting whether to
> enable optional architecture or ABI features for a new ELF process.
I think this is an earlier version of this feature? (e.g. I had suggested
WARN_ON_ONCE()) Perhaps we should try to merge this ahead of the CET
and BTI patches, just so there isn't a forked discussion?
-Kees
>
> For now, there are no generic properties that we care about, so do
> nothing unless CONFIG_ARCH_USE_GNU_PROPERTY=y.
>
> Otherwise, the presence of properties using the PT_PROGRAM_PROPERTY
> phdrs entry (if any), and notify each property to the arch code.
>
> For now, the added code is not used.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> fs/binfmt_elf.c | 127 +++++++++++++++++++++++++++++++++++++++
> fs/compat_binfmt_elf.c | 4 ++
> include/linux/elf.h | 19 ++++++
> include/uapi/linux/elf.h | 4 ++
> 4 files changed, 154 insertions(+)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index ecd8d2698515..054446f93442 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -39,12 +39,18 @@
> #include <linux/sched/coredump.h>
> #include <linux/sched/task_stack.h>
> #include <linux/sched/cputime.h>
> +#include <linux/sizes.h>
> +#include <linux/types.h>
> #include <linux/cred.h>
> #include <linux/dax.h>
> #include <linux/uaccess.h>
> #include <asm/param.h>
> #include <asm/page.h>
>
> +#ifndef ELF_COMPAT
> +#define ELF_COMPAT 0
> +#endif
> +
> #ifndef user_long_t
> #define user_long_t long
> #endif
> @@ -678,6 +684,111 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
> * libraries. There is no binary dependent code anywhere else.
> */
>
> +static int parse_elf_property(const char *data, size_t *off, size_t datasz,
> + struct arch_elf_state *arch,
> + bool have_prev_type, u32 *prev_type)
> +{
> + size_t o, step;
> + const struct gnu_property *pr;
> + int ret;
> +
> + if (*off == datasz)
> + return -ENOENT;
> +
> + if (WARN_ON(*off > datasz || *off % ELF_GNU_PROPERTY_ALIGN))
> + return -EIO;
> + o = *off;
> + datasz -= *off;
> +
> + if (datasz < sizeof(*pr))
> + return -EIO;
> + pr = (const struct gnu_property *)(data + o);
> + o += sizeof(*pr);
> + datasz -= sizeof(*pr);
> +
> + if (pr->pr_datasz > datasz)
> + return -EIO;
> +
> + WARN_ON(o % ELF_GNU_PROPERTY_ALIGN);
> + step = round_up(pr->pr_datasz, ELF_GNU_PROPERTY_ALIGN);
> + if (step > datasz)
> + return -EIO;
> +
> + /* Properties are supposed to be unique and sorted on pr_type: */
> + if (have_prev_type && pr->pr_type <= *prev_type)
> + return -EIO;
> + *prev_type = pr->pr_type;
> +
> + ret = arch_parse_elf_property(pr->pr_type, data + o,
> + pr->pr_datasz, ELF_COMPAT, arch);
> + if (ret)
> + return ret;
> +
> + *off = o + step;
> + return 0;
> +}
> +
> +#define NOTE_DATA_SZ SZ_1K
> +#define GNU_PROPERTY_TYPE_0_NAME "GNU"
> +#define NOTE_NAME_SZ (sizeof(GNU_PROPERTY_TYPE_0_NAME))
> +
> +static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
> + struct arch_elf_state *arch)
> +{
> + union {
> + struct elf_note nhdr;
> + char data[NOTE_DATA_SZ];
> + } note;
> + loff_t pos;
> + ssize_t n;
> + size_t off, datasz;
> + int ret;
> + bool have_prev_type;
> + u32 prev_type;
> +
> + if (!IS_ENABLED(CONFIG_ARCH_USE_GNU_PROPERTY) || !phdr)
> + return 0;
> +
> + /* load_elf_binary() shouldn't call us unless this is true... */
> + if (WARN_ON(phdr->p_type != PT_GNU_PROPERTY))
> + return -EIO;
> +
> + /* If the properties are crazy large, that's too bad (for now): */
> + if (phdr->p_filesz > sizeof(note))
> + return -ENOEXEC;
> +
> + pos = phdr->p_offset;
> + n = kernel_read(f, ¬e, phdr->p_filesz, &pos);
> +
> + BUILD_BUG_ON(sizeof(note) < sizeof(note.nhdr) + NOTE_NAME_SZ);
> + if (n < 0 || n < sizeof(note.nhdr) + NOTE_NAME_SZ)
> + return -EIO;
> +
> + if (note.nhdr.n_type != NT_GNU_PROPERTY_TYPE_0 ||
> + note.nhdr.n_namesz != NOTE_NAME_SZ ||
> + strncmp(note.data + sizeof(note.nhdr),
> + GNU_PROPERTY_TYPE_0_NAME, n - sizeof(note.nhdr)))
> + return -EIO;
> +
> + off = round_up(sizeof(note.nhdr) + NOTE_NAME_SZ,
> + ELF_GNU_PROPERTY_ALIGN);
> + if (off > n)
> + return -EIO;
> +
> + if (note.nhdr.n_descsz > n - off)
> + return -EIO;
> + datasz = off + note.nhdr.n_descsz;
> +
> + have_prev_type = false;
> + do {
> + ret = parse_elf_property(note.data, &off, datasz, arch,
> + have_prev_type, &prev_type);
> + have_prev_type = true;
> + } while (!ret);
> +
> + return ret == -ENOENT ? 0 : ret;
> +}
> +
> static int load_elf_binary(struct linux_binprm *bprm)
> {
> struct file *interpreter = NULL; /* to shut gcc up */
> @@ -685,6 +796,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> int load_addr_set = 0;
> unsigned long error;
> struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
> + struct elf_phdr *elf_property_phdata = NULL;
> unsigned long elf_bss, elf_brk;
> int bss_prot = 0;
> int retval, i;
> @@ -731,6 +843,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
> char *elf_interpreter;
>
> + if (elf_ppnt->p_type == PT_GNU_PROPERTY) {
> + elf_property_phdata = elf_ppnt;
> + continue;
> + }
> +
> if (elf_ppnt->p_type != PT_INTERP)
> continue;
>
> @@ -818,9 +935,14 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
>
> /* Pass PT_LOPROC..PT_HIPROC headers to arch code */
> + elf_property_phdata = NULL;
> elf_ppnt = interp_elf_phdata;
> for (i = 0; i < loc->interp_elf_ex.e_phnum; i++, elf_ppnt++)
> switch (elf_ppnt->p_type) {
> + case PT_GNU_PROPERTY:
> + elf_property_phdata = elf_ppnt;
> + break;
> +
> case PT_LOPROC ... PT_HIPROC:
> retval = arch_elf_pt_proc(&loc->interp_elf_ex,
> elf_ppnt, interpreter,
> @@ -831,6 +953,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> }
> }
>
> + retval = parse_elf_properties(interpreter ?: bprm->file,
> + elf_property_phdata, &arch_state);
> + if (retval)
> + goto out_free_dentry;
> +
> /*
> * Allow arch code to reject the ELF at this point, whilst it's
> * still possible to return an error to the code that invoked
> diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
> index aaad4ca1217e..13a087bc816b 100644
> --- a/fs/compat_binfmt_elf.c
> +++ b/fs/compat_binfmt_elf.c
> @@ -17,6 +17,8 @@
> #include <linux/elfcore-compat.h>
> #include <linux/time.h>
>
> +#define ELF_COMPAT 1
> +
> /*
> * Rename the basic ELF layout types to refer to the 32-bit class of files.
> */
> @@ -28,11 +30,13 @@
> #undef elf_shdr
> #undef elf_note
> #undef elf_addr_t
> +#undef ELF_GNU_PROPERTY_ALIGN
> #define elfhdr elf32_hdr
> #define elf_phdr elf32_phdr
> #define elf_shdr elf32_shdr
> #define elf_note elf32_note
> #define elf_addr_t Elf32_Addr
> +#define ELF_GNU_PROPERTY_ALIGN ELF32_GNU_PROPERTY_ALIGN
>
> /*
> * Some data types as stored in coredump.
> diff --git a/include/linux/elf.h b/include/linux/elf.h
> index 459cddcceaac..7bdc6da160c7 100644
> --- a/include/linux/elf.h
> +++ b/include/linux/elf.h
> @@ -22,6 +22,9 @@
> SET_PERSONALITY(ex)
> #endif
>
> +#define ELF32_GNU_PROPERTY_ALIGN 4
> +#define ELF64_GNU_PROPERTY_ALIGN 8
> +
> #if ELF_CLASS == ELFCLASS32
>
> extern Elf32_Dyn _DYNAMIC [];
> @@ -32,6 +35,7 @@ extern Elf32_Dyn _DYNAMIC [];
> #define elf_addr_t Elf32_Off
> #define Elf_Half Elf32_Half
> #define Elf_Word Elf32_Word
> +#define ELF_GNU_PROPERTY_ALIGN ELF32_GNU_PROPERTY_ALIGN
>
> #else
>
> @@ -43,6 +47,7 @@ extern Elf64_Dyn _DYNAMIC [];
> #define elf_addr_t Elf64_Off
> #define Elf_Half Elf64_Half
> #define Elf_Word Elf64_Word
> +#define ELF_GNU_PROPERTY_ALIGN ELF64_GNU_PROPERTY_ALIGN
>
> #endif
>
> @@ -64,4 +69,18 @@ struct gnu_property {
> u32 pr_datasz;
> };
>
> +struct arch_elf_state;
> +
> +#ifndef CONFIG_ARCH_USE_GNU_PROPERTY
> +static inline int arch_parse_elf_property(u32 type, const void *data,
> + size_t datasz, bool compat,
> + struct arch_elf_state *arch)
> +{
> + return 0;
> +}
> +#else
> +extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
> + bool compat, struct arch_elf_state *arch);
> +#endif
> +
> #endif /* _LINUX_ELF_H */
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index 61251ecabdd7..518651708d8f 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -368,6 +368,7 @@ typedef struct elf64_shdr {
> * Notes used in ET_CORE. Architectures export some of the arch register sets
> * using the corresponding note types via the PTRACE_GETREGSET and
> * PTRACE_SETREGSET requests.
> + * The note name for all these is "LINUX".
> */
> #define NT_PRSTATUS 1
> #define NT_PRFPREG 2
> @@ -430,6 +431,9 @@ typedef struct elf64_shdr {
> #define NT_MIPS_FP_MODE 0x801 /* MIPS floating-point mode */
> #define NT_MIPS_MSA 0x802 /* MIPS SIMD registers */
>
> +/* Note types with note name "GNU" */
> +#define NT_GNU_PROPERTY_TYPE_0 5
> +
> /* Note header in a PT_NOTE section */
> typedef struct elf32_note {
> Elf32_Word n_namesz; /* Name size */
> --
> 2.21.0
>
--
Kees Cook
next prev parent reply other threads:[~2020-02-25 21:20 UTC|newest]
Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 18:19 [RFC PATCH v9 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2020-02-06 0:16 ` Randy Dunlap
2020-02-06 20:17 ` Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-28 15:55 ` Yu-cheng Yu
2020-02-26 17:57 ` Dave Hansen
2020-03-09 17:00 ` Yu-cheng Yu
2020-03-09 17:21 ` Dave Hansen
2020-03-09 19:27 ` Yu-cheng Yu
2020-03-09 19:35 ` Dave Hansen
2020-03-09 19:50 ` H.J. Lu
2020-03-09 20:16 ` Andy Lutomirski
2020-03-09 20:54 ` H.J. Lu
2020-03-09 20:59 ` Dave Hansen
2020-03-09 21:12 ` H.J. Lu
2020-03-09 22:02 ` Andy Lutomirski
2020-03-09 22:19 ` Dave Hansen
2020-03-09 23:11 ` H.J. Lu
2020-03-09 23:20 ` Dave Hansen
2020-03-09 23:51 ` H.J. Lu
2020-03-09 23:59 ` Andy Lutomirski
2020-03-10 0:08 ` H.J. Lu
2020-03-10 1:21 ` Andy Lutomirski
2020-03-10 2:13 ` H.J. Lu
2020-02-05 18:19 ` [RFC PATCH v9 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-02-25 20:04 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 04/27] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-02-25 20:06 ` Kees Cook
2020-02-26 17:10 ` Dave Hansen
2020-03-05 20:44 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 17:03 ` Dave Hansen
2020-02-26 19:57 ` Pavel Machek
2020-03-05 20:38 ` Yu-cheng Yu
2020-02-26 18:05 ` Dave Hansen
2020-02-27 1:02 ` H.J. Lu
2020-02-27 1:16 ` Dave Hansen
2020-02-27 2:11 ` H.J. Lu
2020-02-27 3:57 ` Andy Lutomirski
2020-02-27 18:03 ` Dave Hansen
2020-03-06 18:37 ` Yu-cheng Yu
2020-03-06 19:02 ` Dave Hansen
2020-03-06 21:16 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 18:07 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 07/27] Add guard pages around a Shadow Stack Yu-cheng Yu
2020-02-25 20:11 ` Kees Cook
2020-02-26 18:17 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 08/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 18:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 09/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 21:35 ` Dave Hansen
2020-04-01 19:08 ` Yu-cheng Yu
2020-04-01 19:22 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-26 22:02 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 11/27] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-02-25 20:13 ` Kees Cook
2020-02-26 22:04 ` Dave Hansen
2020-04-03 15:42 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:14 ` Kees Cook
2020-02-26 22:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-02-25 20:16 ` Kees Cook
2020-02-26 22:47 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 14/27] mm: Handle Shadow Stack page fault Yu-cheng Yu
2020-02-25 20:20 ` Kees Cook
2020-03-05 18:30 ` Yu-cheng Yu
2020-02-27 0:08 ` Dave Hansen
2020-04-07 18:14 ` Yu-cheng Yu
2020-04-07 22:21 ` Dave Hansen
2020-04-08 18:18 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2020-02-25 20:59 ` Kees Cook
2020-03-13 22:00 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack Yu-cheng Yu
2020-02-27 0:34 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support Yu-cheng Yu
2020-02-25 21:07 ` Kees Cook
2020-02-27 0:55 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2020-02-25 21:10 ` Kees Cook
2020-03-05 18:39 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 19/27] x86/cet/shstk: Handle signals for Shadow Stack Yu-cheng Yu
2020-02-25 21:17 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 20/27] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 21/27] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND Yu-cheng Yu
2020-02-25 21:18 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-02-25 21:20 ` Kees Cook [this message]
2020-02-05 18:19 ` [RFC PATCH v9 23/27] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack Yu-cheng Yu
2020-02-25 21:22 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-02-25 21:29 ` Kees Cook
2020-03-25 21:51 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 26/27] mm/mmap: Add Shadow Stack pages to memory accounting Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 27/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2020-02-25 21:31 ` [RFC PATCH v9 00/27] Control-flow Enforcement: " 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=202002251319.030E727E99@keescook \
--to=keescook@chromium.org \
--cc=Dave.Martin@arm.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=bsingharora@gmail.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=esyr@redhat.com \
--cc=fweimer@redhat.com \
--cc=gorcunov@gmail.com \
--cc=hjl.tools@gmail.com \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=nadav.amit@gmail.com \
--cc=oleg@redhat.com \
--cc=pavel@ucw.cz \
--cc=peterz@infradead.org \
--cc=ravi.v.shankar@intel.com \
--cc=rdunlap@infradead.org \
--cc=tglx@linutronix.de \
--cc=vedvyas.shanbhogue@intel.com \
--cc=x86-patch-review@intel.com \
--cc=x86@kernel.org \
--cc=yu-cheng.yu@intel.com \
/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 NNTP newsgroup(s).