LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Alexander Potapenko <glider@google.com>
To: dave.hansen@linux.intel.com, mingo@kernel.org,
	kirill.shutemov@linux.intel.com
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	mka@chromium.org, dvyukov@google.com, md@google.com
Subject: [PATCH v2] x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte_mask'
Date: Tue,  8 May 2018 18:28:29 +0200	[thread overview]
Message-ID: <20180508162829.7729-1-glider@google.com> (raw)

Clang builds with defconfig started crashing after commit fb43d6cb91ef
("x86/mm: Do not auto-massage page protections")
This was caused by introducing a new global access in __startup_64().

Code in __startup_64() can be relocated during execution, but the compiler
doesn't have to generate PC-relative relocations when accessing globals
from that function. Clang actually does not generate them, which leads
to boot-time crashes. To work around this problem, every global pointer
must be adjusted using fixup_pointer().

Signed-off-by: Alexander Potapenko <glider@google.com>
Fixes: fb43d6cb91ef ("x86/mm: Do not auto-massage page protections")
---
 v2: better patch description, added a comment to __startup_64()
---
 arch/x86/kernel/head64.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 0c408f8c4ed4..9223792f6d0e 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -104,6 +104,13 @@ static bool __head check_la57_support(unsigned long physaddr)
 }
 #endif
 
+
+/* Code in __startup_64() can be relocated during execution, but the compiler
+ * doesn't have to generate PC-relative relocations when accessing globals from
+ * that function. Clang actually does not generate them, which leads to
+ * boot-time crashes. To work around this problem, every global pointer must
+ * be adjusted using fixup_pointer().
+ */
 unsigned long __head __startup_64(unsigned long physaddr,
 				  struct boot_params *bp)
 {
@@ -113,6 +120,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	p4dval_t *p4d;
 	pudval_t *pud;
 	pmdval_t *pmd, pmd_entry;
+	pteval_t *mask_ptr;
 	bool la57;
 	int i;
 	unsigned int *next_pgt_ptr;
@@ -196,7 +204,8 @@ unsigned long __head __startup_64(unsigned long physaddr,
 
 	pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL;
 	/* Filter out unsupported __PAGE_KERNEL_* bits: */
-	pmd_entry &= __supported_pte_mask;
+	mask_ptr = (pteval_t *)fixup_pointer(&__supported_pte_mask, physaddr);
+	pmd_entry &= *mask_ptr;
 	pmd_entry += sme_get_me_mask();
 	pmd_entry +=  physaddr;
 
-- 
2.17.0.441.gb46fe60e1d-goog

             reply	other threads:[~2018-05-08 16:28 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-08 16:28 Alexander Potapenko [this message]
2018-05-08 16:49 ` Dave Hansen
2018-05-08 21:44 ` Kirill A. Shutemov
2018-05-09  9:16   ` Alexander Potapenko

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=20180508162829.7729-1-glider@google.com \
    --to=glider@google.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=dvyukov@google.com \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=md@google.com \
    --cc=mingo@kernel.org \
    --cc=mka@chromium.org \
    --subject='Re: [PATCH v2] x86/boot/64/clang: Use fixup_pointer() to access '\''__supported_pte_mask'\''' \
    /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

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).