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Date: Fri, 25 Sep 2020 22:01:15 +0200 From: Borislav Petkov <bp@...en8.de> To: Mark Mossberg <mark.mossberg@...il.com> Cc: tglx@...utronix.de, mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com, jannh@...gle.com Subject: Re: [PATCH] x86/dumpstack: Fix misleading instruction pointer error message On Fri, Sep 25, 2020 at 07:31:51PM +0000, Mark Mossberg wrote: > Unconditionally 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. This is > because copy_code() calls copy_from_user_nmi() for userspace pointers, > which disables page fault handling. > > This is reproducible in OOM situations, where it's plausible that the > code may be reclaimed in the time between entry into the kernel and when > this message is printed. This leaves a misleading log in dmesg that > suggests instruction pointer corruption has occurred, which may alarm > users. > > This patch changes the message printed for userspace pointers to more > accurately reflect the possible reasons why the code cannot be dumped. > > Signed-off-by: Mark Mossberg <mark.mossberg@...il.com> > --- > arch/x86/kernel/dumpstack.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c > index 48ce44576947..37dbf16c7456 100644 > --- a/arch/x86/kernel/dumpstack.c > +++ b/arch/x86/kernel/dumpstack.c > @@ -115,7 +115,10 @@ 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); I'd prefer if this thing said exactly what the problem is: printk("%sCode: Unable to access opcode bytes at rIP 0x%lx... " or so. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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