Hello Josh and Steven!
On 10/22/2025 4:43 PM, Jens Remus wrote:
> From: Josh Poimboeuf <[email protected]>
>
> In preparation for unwinding user space stacks with sframe, add basic
> sframe compile infrastructure and support for reading the .sframe
> section header.
>
> sframe_add_section() reads the header and unconditionally returns an
> error, so it's not very useful yet. A subsequent patch will improve
> that.
>
> Link:
> https://lore.kernel.org/all/f27e8463783febfa0dabb0432a3dd6be8ad98412.1737511963.git.jpoim...@kernel.org/
>
> [ Jens Remus: Add support for PC-relative FDE function start address. ]
I took a closer look and wondered whether some parts should better be
moved to subsequent patches.
> diff --git a/include/linux/sframe.h b/include/linux/sframe.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_SFRAME_H
> +#define _LINUX_SFRAME_H
> +
> +#include <linux/mm_types.h>
Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data
in per-mm maple tree".
> +#include <linux/unwind_user_types.h>
Move to "[PATCH v11 06/15] unwind_user/sframe: Add support for reading
.sframe contents". find_sframe() needs the types.
> +
> +#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
> +
> +struct sframe_section {
> + unsigned long sframe_start;
> + unsigned long sframe_end;
> + unsigned long text_start;
> + unsigned long text_end;
> +
> + unsigned long fdes_start;
> + unsigned long fres_start;
> + unsigned long fres_end;
> + unsigned int num_fdes;
> +
> + signed char ra_off;
> + signed char fp_off;
> +};
> +
> +extern int sframe_add_section(unsigned long sframe_start, unsigned long
> sframe_end,
> + unsigned long text_start, unsigned long text_end);
> +extern int sframe_remove_section(unsigned long sframe_addr);
> +
> +#else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */
> +
> +static inline int sframe_add_section(unsigned long sframe_start, unsigned
> long sframe_end,
> + unsigned long text_start, unsigned long
> text_end)
> +{
> + return -ENOSYS;
> +}
> +static inline int sframe_remove_section(unsigned long sframe_addr) { return
> -ENOSYS; }
> +
> +#endif /* CONFIG_HAVE_UNWIND_USER_SFRAME */
> +
> +#endif /* _LINUX_SFRAME_H */
> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> @@ -0,0 +1,137 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Userspace sframe access functions
> + */
> +
> +#define pr_fmt(fmt) "sframe: " fmt
> +
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/srcu.h>
> +#include <linux/uaccess.h>
> +#include <linux/mm.h>
Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data
in per-mm maple tree".
> +#include <linux/string_helpers.h>
> +#include <linux/sframe.h>
> +#include <linux/unwind_user_types.h>
> +
> +#include "sframe.h"
> +
> +#define dbg(fmt, ...)
> \
> + pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
> +
> +static void free_section(struct sframe_section *sec)
> +{
> + kfree(sec);
> +}
> +
> +static int sframe_read_header(struct sframe_section *sec)
> +{
> + unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end;
> + struct sframe_header shdr;
> + unsigned int num_fdes;
> +
> + if (copy_from_user(&shdr, (void __user *)sec->sframe_start,
> sizeof(shdr))) {
> + dbg("header usercopy failed\n");
> + return -EFAULT;
> + }
> +
> + if (shdr.preamble.magic != SFRAME_MAGIC ||
> + shdr.preamble.version != SFRAME_VERSION_2 ||
> + !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
> + !(shdr.preamble.flags & SFRAME_F_FDE_FUNC_START_PCREL) ||
> + shdr.auxhdr_len) {
> + dbg("bad/unsupported sframe header\n");
> + return -EINVAL;
> + }
> +
> + if (!shdr.num_fdes || !shdr.num_fres) {
> + dbg("no fde/fre entries\n");
> + return -EINVAL;
> + }
> +
> + header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr);
> + if (header_end >= sec->sframe_end) {
> + dbg("header doesn't fit in section\n");
> + return -EINVAL;
> + }
> +
> + num_fdes = shdr.num_fdes;
> + fdes_start = header_end + shdr.fdes_off;
> + fdes_end = fdes_start + (num_fdes * sizeof(struct sframe_fde));
> +
> + fres_start = header_end + shdr.fres_off;
> + fres_end = fres_start + shdr.fre_len;
> +
> + if (fres_start < fdes_end || fres_end > sec->sframe_end) {
> + dbg("inconsistent fde/fre offsets\n");
> + return -EINVAL;
> + }
> +
> + sec->num_fdes = num_fdes;
> + sec->fdes_start = fdes_start;
> + sec->fres_start = fres_start;
> + sec->fres_end = fres_end;
> +
> + sec->ra_off = shdr.cfa_fixed_ra_offset;
> + sec->fp_off = shdr.cfa_fixed_fp_offset;
> +
> + return 0;
> +}
> +
> +int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
> + unsigned long text_start, unsigned long text_end)
> +{
> + struct maple_tree *sframe_mt = ¤t->mm->sframe_mt;
Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data
in per-mm maple tree".
> + struct vm_area_struct *sframe_vma, *text_vma;
> + struct mm_struct *mm = current->mm;
> + struct sframe_section *sec;
> + int ret;
> +
> + if (!sframe_start || !sframe_end || !text_start || !text_end) {
> + dbg("zero-length sframe/text address\n");
> + return -EINVAL;
> + }
> +
> + scoped_guard(mmap_read_lock, mm) {
> + sframe_vma = vma_lookup(mm, sframe_start);
> + if (!sframe_vma || sframe_end > sframe_vma->vm_end) {
> + dbg("bad sframe address (0x%lx - 0x%lx)\n",
> + sframe_start, sframe_end);
> + return -EINVAL;
> + }
> +
> + text_vma = vma_lookup(mm, text_start);
> + if (!text_vma ||
> + !(text_vma->vm_flags & VM_EXEC) ||
> + text_end > text_vma->vm_end) {
> + dbg("bad text address (0x%lx - 0x%lx)\n",
> + text_start, text_end);
> + return -EINVAL;
> + }
> + }
> +
> + sec = kzalloc(sizeof(*sec), GFP_KERNEL);
> + if (!sec)
> + return -ENOMEM;
> +
> + sec->sframe_start = sframe_start;
> + sec->sframe_end = sframe_end;
> + sec->text_start = text_start;
> + sec->text_end = text_end;
> +
> + ret = sframe_read_header(sec);
> + if (ret)
> + goto err_free;
> +
> + /* TODO nowhere to store it yet - just free it and return an error */
An alternative would be to move sframe_add_section() to
"[PATCH v11 04/15] unwind_user/sframe: Store sframe section data in
per-mm maple tree" and reorder the patches as outlined below.
> + ret = -ENOSYS;
> +
> +err_free:
> + free_section(sec);
> + return ret;
> +}
> +
> +int sframe_remove_section(unsigned long sframe_start)
> +{
> + return -ENOSYS;
> +}
I wonder whether the series should be restructured as follows:
unwind_user/sframe: Store .sframe section data in per-mm maple tree
unwind_user/sframe: Detect .sframe sections in executables
unwind_user/sframe: Add support for reading .sframe headers
unwind_user/sframe: Add support for reading .sframe contents
unwind_user/sframe: Wire up unwind_user to sframe
x86/uaccess: Add unsafe_copy_from_user() implementation
unwind_user/sframe/x86: Enable sframe unwinding on x86
unwind_user: Stop when reaching an outermost frame
unwind_user/sframe: Add support for outermost frame indication
unwind_user/sframe: Remove .sframe section on detected corruption
unwind_user/sframe: Show file name in debug output
unwind_user/sframe: Add .sframe validation option
unwind_user/sframe: Add prctl() interface for registering .sframe sections
While moving sframe_add_section() and sframe_remove_section() from
"unwind_user/sframe: Add support for reading .sframe headers" to
"unwind_user/sframe: Store .sframe section data in per-mm maple tree" or
into a new second patch, as they depend on the first and are required
by the third.
What are your thoughts? The reordering might be wasted effort.
Thanks and regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
[email protected]
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