From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <namit@vmware.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jiri Kosina <jkosina@suse.cz>, Andy Lutomirski <luto@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes
Date: Thu, 6 Sep 2018 10:42:56 +0200 [thread overview]
Message-ID: <20180906084256.GE24142@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180906081300.GF24082@hirez.programming.kicks-ass.net>
On Thu, Sep 06, 2018 at 10:13:00AM +0200, Peter Zijlstra wrote:
> No, you got it the first time. There are in fact more fixmap abusers;
> see drivers/acpi/apei/ghes.c. Also, as long as set_fixmap() allows
> overwriting a _PAGE_PRESENT pte and has that dodgy
> __flush_tlb_one_kernel() in it, the broken remains (and can return).
>
> So we need to fix fixmap, to either disallow overwriting a _PAGE_PRESENT
> pte, or to issue a full TLB invalidate.
>
> Either fix will terminally break GHES, but that's OK, they've known
> about this issue since 2015 and haven't cared, so I can't be bothered
> about them.
Worse, when I boot with the below patch in, I get hits on text_poke (we
knew about this), but I also get hits from:
release_ds_buffer()
Because PEBS/BTS hardware write through the page-tables (I know right),
their buffers need to be in the PTI user map, and we do that by mapping
the pages in the CAE, and that uses fixmap.
---
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index dd519f372169..20dcd6fa690e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -259,9 +259,16 @@ static pte_t *fill_pte(pmd_t *pmd, unsigned long vaddr)
static void __set_pte_vaddr(pud_t *pud, unsigned long vaddr, pte_t new_pte)
{
pmd_t *pmd = fill_pmd(pud, vaddr);
- pte_t *pte = fill_pte(pmd, vaddr);
+ pte_t *ptep = fill_pte(pmd, vaddr);
- set_pte(pte, new_pte);
+ pte_t pte = *ptep;
+
+ set_pte(ptep, new_pte);
+
+ WARN((pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) != pte_val(new_pte)),
+ "set_fixmap(%d, %lx), was: %lx",
+ (int)__virt_to_fix(vaddr),
+ pte_val(new_pte), pte_val(pte));
/*
* It's enough to flush this one mapping.
next prev parent reply other threads:[~2018-09-06 8:42 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-02 17:32 [PATCH v2 0/6] x86/alternatives: text_poke() fixes Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:58 ` Nadav Amit
2018-09-06 19:58 ` Nadav Amit
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:57 ` Nadav Amit
2018-09-06 20:57 ` Nadav Amit
2018-09-06 21:41 ` Peter Zijlstra
2018-09-06 21:41 ` Peter Zijlstra
2018-09-02 17:32 ` [PATCH v2 2/6] x86/mm: temporary mm struct Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 3/6] fork: provide a function for copying init_mm Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 4/6] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 9:01 ` Peter Zijlstra
2018-09-06 9:01 ` Peter Zijlstra
2018-09-07 20:52 ` Nadav Amit
2018-09-07 20:52 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 5/6] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 6/6] x86/alternatives: remove text_poke() return value Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-05 18:56 ` [PATCH v2 0/6] x86/alternatives: text_poke() fixes Peter Zijlstra
2018-09-05 18:56 ` Peter Zijlstra
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra [this message]
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:58 ` Nadav Amit
2018-09-06 17:58 ` Nadav Amit
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:38 ` Nadav Amit
2018-09-06 18:38 ` Nadav Amit
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
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