From: Oleg Nesterov <oleg@redhat.com>
To: Mark Mossberg <mark.mossberg@gmail.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
x86@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com,
jannh@google.com, kyin@redhat.com
Subject: Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message
Date: Tue, 3 Nov 2020 13:50:34 +0100 [thread overview]
Message-ID: <20201103125034.GA30391@redhat.com> (raw)
In-Reply-To: <20201002042915.403558-1-mark.mossberg@gmail.com>
On 10/02, Mark Mossberg wrote:
>
> Printing "Bad RIP value" if copy_code() fails can be misleading for
> userspace pointers, since copy_code() can fail if the instruction
> pointer is valid, but the code is paged out.
Another problem is that show_opcodes() makes no sense if user_mode(regs)
and tsk is not current. Try "echo t > /proc/sysrq-trigger".
In this case copy_from_user_nmi() will either fail, or (worse) it will
read the "random" memory from current->mm.
Perhaps we can add something like
if (user_mode(regs) && regs != task_pt_regs(current))
return;
at the start of show_opcodes() ?
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -115,7 +115,8 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
> unsigned long prologue = regs->ip - PROLOGUE_SIZE;
>
> if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
> - printk("%sCode: Bad RIP value.\n", loglvl);
> + printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
> + loglvl, prologue);
> } else {
> printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
> __stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes,
> --
> 2.25.1
>
next prev parent reply other threads:[~2020-11-03 12:50 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 4:29 [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message Mark Mossberg
2020-10-02 10:26 ` [tip: x86/core] " tip-bot2 for Mark Mossberg
2020-11-03 12:50 ` Oleg Nesterov [this message]
2020-11-03 17:15 ` [PATCH v2] " Borislav Petkov
2020-11-03 17:47 ` Oleg Nesterov
2020-11-03 17:52 ` Borislav Petkov
2020-11-03 18:11 ` Oleg Nesterov
2020-11-03 18:20 ` Borislav Petkov
2020-11-16 22:01 ` Thomas Gleixner
2020-11-16 23:04 ` Andy Lutomirski
2020-11-16 23:37 ` Thomas Gleixner
2020-11-17 3:29 ` Andy Lutomirski
2020-11-17 9:54 ` Borislav Petkov
2020-11-17 17:31 ` Oleg Nesterov
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=20201103125034.GA30391@redhat.com \
--to=oleg@redhat.com \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=kyin@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.mossberg@gmail.com \
--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 NNTP newsgroup(s).