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authorChang S. Bae <chang.seok.bae@intel.com>2019-06-16 18:44:11 +0300
committerThomas Gleixner <tglx@linutronix.de>2019-06-22 12:38:50 +0300
commit48f5e52e916b55fb73754833efbacc7f8081a159 (patch)
tree89ca5b55d3fb55517789e8d8bdec80727ee0e9fa /arch/x86/kernel/ptrace.c
parentb302e4b176d00e1cbc80148c5d0aee36751f7480 (diff)
downloadlinux-48f5e52e916b55fb73754833efbacc7f8081a159.tar.xz
x86/ptrace: Prevent ptrace from clearing the FS/GS selector
When a ptracer writes a ptracee's FS/GSBASE with a different value, the selector is also cleared. This behavior is not correct as the selector should be preserved. Update only the base value and leave the selector intact. To simplify the code further remove the conditional checking for the same value as this code is not performance critical. The only recognizable downside of this change is when the selector is already nonzero on write. The base will be reloaded according to the selector. But the case is highly unexpected in real usages. [ tglx: Massage changelog ] Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: "H . Peter Anvin" <hpa@zytor.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Link: https://lkml.kernel.org/r/9040CFCD-74BD-4C17-9A01-B9B713CF6B10@intel.com
Diffstat (limited to 'arch/x86/kernel/ptrace.c')
-rw-r--r--arch/x86/kernel/ptrace.c14
1 files changed, 2 insertions, 12 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index a166c960bc9e..3108cdc00b29 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -397,22 +397,12 @@ static int putreg(struct task_struct *child,
case offsetof(struct user_regs_struct,fs_base):
if (value >= TASK_SIZE_MAX)
return -EIO;
- /*
- * When changing the FS base, use do_arch_prctl_64()
- * to set the index to zero and to set the base
- * as requested.
- */
- if (child->thread.fsbase != value)
- return do_arch_prctl_64(child, ARCH_SET_FS, value);
+ x86_fsbase_write_task(child, value);
return 0;
case offsetof(struct user_regs_struct,gs_base):
- /*
- * Exactly the same here as the %fs handling above.
- */
if (value >= TASK_SIZE_MAX)
return -EIO;
- if (child->thread.gsbase != value)
- return do_arch_prctl_64(child, ARCH_SET_GS, value);
+ x86_gsbase_write_task(child, value);
return 0;
#endif
}