Messages in this thread Patch in this message | | | Date | Fri, 15 May 2015 10:05:32 +0200 | From | Willy Tarreau <> | Subject | [ 02/48] x86/tls: Validate TLS entries to protect espfix |
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2.6.32-longterm review patch. If anyone has any objections, please let me know.
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From: Andy Lutomirski <luto@amacapital.net>
commit 41bdc78544b8a93a9c6814b8bbbfef966272abbe upstream
Installing a 16-bit RW data segment into the GDT defeats espfix. AFAICT this will not affect glibc, Wine, or dosemu at all.
Signed-off-by: Andy Lutomirski <luto@amacapital.net> Acked-by: H. Peter Anvin <hpa@zytor.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: security@kernel.org <security@kernel.org> Cc: Willy Tarreau <w@1wt.eu> Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Willy Tarreau <w@1wt.eu> --- arch/x86/kernel/tls.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c index bcfec2d..7af7338 100644 --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -28,6 +28,21 @@ static int get_free_idx(void) return -ESRCH; } +static bool tls_desc_okay(const struct user_desc *info) +{ + if (LDT_empty(info)) + return true; + + /* + * espfix is required for 16-bit data segments, but espfix + * only works for LDT segments. + */ + if (!info->seg_32bit) + return false; + + return true; +} + static void set_tls_desc(struct task_struct *p, int idx, const struct user_desc *info, int n) { @@ -67,6 +82,9 @@ int do_set_thread_area(struct task_struct *p, int idx, if (copy_from_user(&info, u_info, sizeof(info))) return -EFAULT; + if (!tls_desc_okay(&info)) + return -EINVAL; + if (idx == -1) idx = info.entry_number; @@ -197,6 +215,7 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset, { struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES]; const struct user_desc *info; + int i; if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) || (pos % sizeof(struct user_desc)) != 0 || @@ -210,6 +229,10 @@ int regset_tls_set(struct task_struct *target, const struct user_regset *regset, else info = infobuf; + for (i = 0; i < count / sizeof(struct user_desc); i++) + if (!tls_desc_okay(info + i)) + return -EINVAL; + set_tls_desc(target, GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)), info, count / sizeof(struct user_desc)); -- 1.7.12.2.21.g234cd45.dirty
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