Commit-ID: d47b50e7a111bb7a56fb1c974728b56209d7f515
Gitweb: http://git.kernel.org/tip/d47b50e7a111bb7a56fb1c974728b56209d7f515
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 7 Apr 2016 17:31:45 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rudolf Marek <r.marek@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/c6e7b507c72ca3bdbf6c7a8a3ceaa0334e873bd9.1460075211.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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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