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Message-ID: <20241029132709.GY14555@noisy.programming.kicks-ass.net>
Date: Tue, 29 Oct 2024 14:27:09 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
Andrii Nakryiko <andrii.nakryiko@...il.com>,
Jens Remus <jremus@...ux.ibm.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Florian Weimer <fweimer@...hat.com>,
Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding
On Mon, Oct 28, 2024 at 02:47:36PM -0700, Josh Poimboeuf wrote:
> +static int __sframe_add_section(unsigned long sframe_addr,
> + unsigned long text_start,
> + unsigned long text_end)
> +{
> + struct maple_tree *sframe_mt = ¤t->mm->sframe_mt;
> + struct sframe_section *sec;
> + struct sframe_header shdr;
> + unsigned long header_end;
> + int ret;
> +
> + if (copy_from_user(&shdr, (void __user *)sframe_addr, sizeof(shdr)))
> + return -EFAULT;
> +
> + if (shdr.preamble.magic != SFRAME_MAGIC ||
> + shdr.preamble.version != SFRAME_VERSION_2 ||
> + !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
> + shdr.auxhdr_len || !shdr.num_fdes || !shdr.num_fres ||
> + shdr.fdes_off > shdr.fres_off) {
> + return -EINVAL;
> + }
> +
> + sec = kmalloc(sizeof(*sec), GFP_KERNEL);
> + if (!sec)
> + return -ENOMEM;
> +
> + header_end = sframe_addr + SFRAME_HDR_SIZE(shdr);
> +
> + sec->sframe_addr = sframe_addr;
> + sec->text_addr = text_start;
> + sec->fdes_addr = header_end + shdr.fdes_off;
> + sec->fres_addr = header_end + shdr.fres_off;
> + sec->fdes_nr = shdr.num_fdes;
> + sec->ra_off = shdr.cfa_fixed_ra_offset;
> + sec->fp_off = shdr.cfa_fixed_fp_offset;
> +
> + ret = mtree_insert_range(sframe_mt, text_start, text_end, sec, GFP_KERNEL);
> + if (ret) {
> + kfree(sec);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +int sframe_add_section(unsigned long sframe_addr, unsigned long text_start,
> + unsigned long text_end)
> +{
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *sframe_vma;
> +
> + mmap_read_lock(mm);
DEFINE_GUARD(mmap_read_lock, struct mm_struct *,
mmap_read_lock(_T), mmap_read_unlock(_T))
in include/linux/mmap_lock.h ?
> +
> + sframe_vma = vma_lookup(mm, sframe_addr);
> + if (!sframe_vma)
> + goto err_unlock;
> +
> + if (text_start && text_end) {
> + struct vm_area_struct *text_vma;
> +
> + text_vma = vma_lookup(mm, text_start);
> + if (!(text_vma->vm_flags & VM_EXEC))
> + goto err_unlock;
> +
> + if (PAGE_ALIGN(text_end) != text_vma->vm_end)
> + goto err_unlock;
> + } else {
> + struct vm_area_struct *vma, *text_vma = NULL;
> + VMA_ITERATOR(vmi, mm, 0);
> +
> + for_each_vma(vmi, vma) {
> + if (vma->vm_file != sframe_vma->vm_file ||
> + !(vma->vm_flags & VM_EXEC))
> + continue;
> +
> + if (text_vma) {
> + pr_warn_once("%s[%d]: multiple EXEC segments unsupported\n",
> + current->comm, current->pid);
> + goto err_unlock;
> + }
> +
> + text_vma = vma;
> + }
> +
> + if (!text_vma)
> + goto err_unlock;
> +
> + text_start = text_vma->vm_start;
> + text_end = text_vma->vm_end;
> + }
> +
> + mmap_read_unlock(mm);
> +
> + return __sframe_add_section(sframe_addr, text_start, text_end);
> +
> +err_unlock:
> + mmap_read_unlock(mm);
> + return -EINVAL;
> +}
> +int sframe_remove_section(unsigned long sframe_addr)
> +{
> + struct mm_struct *mm = current->mm;
> + struct sframe_section *sec;
> + unsigned long index = 0;
> +
> + mt_for_each(&mm->sframe_mt, sec, index, ULONG_MAX) {
> + if (sec->sframe_addr == sframe_addr)
> + return __sframe_remove_section(mm, sec);
> + }
> +
> + return -EINVAL;
> +}
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -64,6 +64,7 @@
> #include <linux/rcupdate.h>
> #include <linux/uidgid.h>
> #include <linux/cred.h>
> +#include <linux/sframe.h>
>
> #include <linux/nospec.h>
>
> @@ -2784,6 +2785,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> case PR_RISCV_SET_ICACHE_FLUSH_CTX:
> error = RISCV_SET_ICACHE_FLUSH_CTX(arg2, arg3);
> break;
> + case PR_ADD_SFRAME:
> + if (arg5)
> + return -EINVAL;
> + error = sframe_add_section(arg2, arg3, arg4);
> + break;
> + case PR_REMOVE_SFRAME:
> + if (arg3 || arg4 || arg5)
> + return -EINVAL;
> + error = sframe_remove_section(arg2);
> + break;
> default:
> error = -EINVAL;
> break;
So I realize that mtree has an internal lock, but are we sure we don't
want a lock around those prctl()s?
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