Re: linux 2.6.27 kernel panic on x86 - please revert commit 3a85e770aa77e4f1a4096275c97b64c10cd7323e

[Suresh Siddha]

On Wed, Oct 15, 2008 at 06:39:39AM -0700, Jeff Chua wrote:
> On Wed, Oct 15, 2008 at 8:05 PM, Ingo Molnar <mingo@xxxxxxx> wrote:
> >> Unsetting CONFIG_COMPAT_VDSO solves the issue.
> >>
> >> Thanks for your help, and sorry for the fault alarm. Did take a while
> >> to trace it down to the commit.
> >
> > hm, setting the option should not break new glibc so this is a
> > regression and we've still got a bug to fix.
> 
> Something must have triggered the bug. Every single linux git update
> has been ok with CONFIG_COMPAT_VDSO=y until now, and I had glibc-2.7
> since Dec 2007.

Jeff, Does the appended patch fix the issue? Thanks.

---
Subject: x86: include USER bit for the PDE_IDENT_ATTR

Jeff Chua reported that this patch

> -#define PTE_IDENT_ATTR  0x007          /* PRESENT+RW+USER */
> -#define PDE_IDENT_ATTR  0x067          /* PRESENT+RW+USER+DIRTY+ACCESSED */
> +#define PTE_IDENT_ATTR  0x003          /* PRESENT+RW */
> +#define PDE_IDENT_ATTR  0x063          /* PRESENT+RW+DIRTY+ACCESSED */

broke kernels with CONFIG_COMPAT_VDSO set with this panic info:

init[1]: segfault at ffffe01c up b7f0dc28 sp bfc26628 error 5 in ld-2.7.90.so[b7f0b000+1c000]

Include USER bit in the PDE_IDENT_ATTR only, as the protection bits
are combined from the PDE and PTE entries. This will allow the high
mapped VDSO page in the case of CONFIG_COMPAT_VDSO to be user
readable.

Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
---

diff --git a/include/asm-x86/pgtable.h b/include/asm-x86/pgtable.h
index 182f9d4..88a53b1 100644
--- a/include/asm-x86/pgtable.h
+++ b/include/asm-x86/pgtable.h
@@ -148,8 +148,13 @@
 #ifdef CONFIG_X86_64
 #define __PAGE_KERNEL_IDENT_LARGE_EXEC	__PAGE_KERNEL_LARGE_EXEC
 #else
+/*
+ * For PDE_IDENT_ATTR include USER bit. As the PDE and PTE protection
+ * bits are combined, this will alow user to access the high address mapped
+ * VDSO in the presence of CONFIG_COMPAT_VDSO
+ */
 #define PTE_IDENT_ATTR	 0x003		/* PRESENT+RW */
-#define PDE_IDENT_ATTR	 0x063		/* PRESENT+RW+DIRTY+ACCESSED */
+#define PDE_IDENT_ATTR	 0x067		/* PRESENT+RW+USER+DIRTY+ACCESSED */
 #define PGD_IDENT_ATTR	 0x001		/* PRESENT (no other attributes) */
 #endif
 


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