Messages in this thread Patch in this message | | | Date | Wed, 13 Apr 2016 04:29:02 -0700 | From | tip-bot for Andy Lutomirski <> | Subject | [tip:x86/asm] x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET_GS |
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Commit-ID: d47b50e7a111bb7a56fb1c974728b56209d7f515 Gitweb: http://git.kernel.org/tip/d47b50e7a111bb7a56fb1c974728b56209d7f515 Author: Andy Lutomirski <luto@kernel.org> AuthorDate: Thu, 7 Apr 2016 17:31:45 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 13 Apr 2016 10:20:41 +0200
x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET_GS
ARCH_GET_FS and ARCH_GET_GS attempted to figure out the fsbase and gsbase respectively from saved thread state. This was wrong: fsbase and gsbase live in registers while a thread is running, not in memory.
For reasons I can't fathom, the fsbase and gsbase code were different. Since neither was correct, I didn't try to figure out what the point of the difference was.
Change it to simply read the MSRs.
The code for reading the base for a remote thread is also completely wrong if the target thread uses its own descriptors (which is the case for all 32-bit threaded programs), but fixing that is a different story.
Signed-off-by: Andy Lutomirski <luto@kernel.org> Reviewed-by: Borislav Petkov <bp@suse.de> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rudolf Marek <r.marek@assembler.cz> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/c6e7b507c72ca3bdbf6c7a8a3ceaa0334e873bd9.1460075211.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/kernel/process_64.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 6cbab31..c671b9b 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -566,10 +566,10 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr) break; case ARCH_GET_FS: { unsigned long base; - if (task->thread.fsindex == FS_TLS_SEL) - base = read_32bit_tls(task, FS_TLS); - else if (doit) + if (doit) rdmsrl(MSR_FS_BASE, base); + else if (task->thread.fsindex == FS_TLS_SEL) + base = read_32bit_tls(task, FS_TLS); else base = task->thread.fs; ret = put_user(base, (unsigned long __user *)addr); @@ -577,16 +577,11 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr) } case ARCH_GET_GS: { unsigned long base; - unsigned gsindex; - if (task->thread.gsindex == GS_TLS_SEL) + if (doit) + rdmsrl(MSR_KERNEL_GS_BASE, base); + else if (task->thread.gsindex == GS_TLS_SEL) base = read_32bit_tls(task, GS_TLS); - else if (doit) { - savesegment(gs, gsindex); - if (gsindex) - rdmsrl(MSR_KERNEL_GS_BASE, base); - else - base = task->thread.gs; - } else + else base = task->thread.gs; ret = put_user(base, (unsigned long __user *)addr); break;
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