Messages in this thread Patch in this message | | | From | Sasha Levin <> | Subject | [PATCH v10 01/18] x86/ptrace: Prevent ptrace from clearing the FS/GS selector | Date | Thu, 23 Apr 2020 19:21:50 -0400 |
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From: "Chang S. Bae" <chang.seok.bae@intel.com>
When a ptracer writes a ptracee's FS/GS base 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.
Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Reviewed-by: Tony Luck <tony.luck@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Andi Kleen <ak@linux.intel.com> Signed-off-by: Sasha Levin <sashal@kernel.org> --- arch/x86/kernel/ptrace.c | 17 ++--------------- 1 file changed, 2 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index f0e1ddbc2fd78..cc56efb75d275 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -380,25 +380,12 @@ 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. - * - * NB: This behavior is nonsensical and likely needs to - * change when FSGSBASE support is added. - */ - 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 } -- 2.20.1
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