176 lines
5.1 KiB
Diff
176 lines
5.1 KiB
Diff
From: Jann Horn <jannh@google.com>
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Date: Sun, 2 Jun 2019 03:15:58 +0200
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Subject: x86/insn-eval: Fix use-after-free access to LDT entry
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Origin: https://git.kernel.org/linus/de9f869616dd95e95c00bdd6b0fcd3421e8a4323
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-13233
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get_desc() computes a pointer into the LDT while holding a lock that
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protects the LDT from being freed, but then drops the lock and returns the
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(now potentially dangling) pointer to its caller.
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Fix it by giving the caller a copy of the LDT entry instead.
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Fixes: 670f928ba09b ("x86/insn-eval: Add utility function to get segment descriptor")
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Cc: stable@vger.kernel.org
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Signed-off-by: Jann Horn <jannh@google.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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arch/x86/lib/insn-eval.c | 47 ++++++++++++++++++++++++-----------------------
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1 file changed, 24 insertions(+), 23 deletions(-)
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diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
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index cf00ab6c6621..306c3a0902ba 100644
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--- a/arch/x86/lib/insn-eval.c
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+++ b/arch/x86/lib/insn-eval.c
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@@ -557,7 +557,8 @@ static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs,
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}
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/**
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- * get_desc() - Obtain pointer to a segment descriptor
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+ * get_desc() - Obtain contents of a segment descriptor
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+ * @out: Segment descriptor contents on success
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* @sel: Segment selector
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*
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* Given a segment selector, obtain a pointer to the segment descriptor.
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@@ -565,18 +566,18 @@ static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs,
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*
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* Returns:
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*
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- * Pointer to segment descriptor on success.
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+ * True on success, false on failure.
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*
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* NULL on error.
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*/
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-static struct desc_struct *get_desc(unsigned short sel)
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+static bool get_desc(struct desc_struct *out, unsigned short sel)
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{
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struct desc_ptr gdt_desc = {0, 0};
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unsigned long desc_base;
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#ifdef CONFIG_MODIFY_LDT_SYSCALL
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if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) {
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- struct desc_struct *desc = NULL;
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+ bool success = false;
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struct ldt_struct *ldt;
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/* Bits [15:3] contain the index of the desired entry. */
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@@ -584,12 +585,14 @@ static struct desc_struct *get_desc(unsigned short sel)
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mutex_lock(¤t->active_mm->context.lock);
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ldt = current->active_mm->context.ldt;
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- if (ldt && sel < ldt->nr_entries)
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- desc = &ldt->entries[sel];
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+ if (ldt && sel < ldt->nr_entries) {
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+ *out = ldt->entries[sel];
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+ success = true;
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+ }
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mutex_unlock(¤t->active_mm->context.lock);
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- return desc;
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+ return success;
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}
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#endif
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native_store_gdt(&gdt_desc);
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@@ -604,9 +607,10 @@ static struct desc_struct *get_desc(unsigned short sel)
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desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK);
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if (desc_base > gdt_desc.size)
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- return NULL;
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+ return false;
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- return (struct desc_struct *)(gdt_desc.address + desc_base);
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+ *out = *(struct desc_struct *)(gdt_desc.address + desc_base);
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+ return true;
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}
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/**
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@@ -628,7 +632,7 @@ static struct desc_struct *get_desc(unsigned short sel)
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*/
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unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx)
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{
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- struct desc_struct *desc;
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+ struct desc_struct desc;
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short sel;
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sel = get_segment_selector(regs, seg_reg_idx);
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@@ -666,11 +670,10 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx)
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if (!sel)
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return -1L;
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- desc = get_desc(sel);
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- if (!desc)
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+ if (!get_desc(&desc, sel))
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return -1L;
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- return get_desc_base(desc);
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+ return get_desc_base(&desc);
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}
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/**
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@@ -692,7 +695,7 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx)
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*/
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static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
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{
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- struct desc_struct *desc;
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+ struct desc_struct desc;
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unsigned long limit;
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short sel;
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@@ -706,8 +709,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
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if (!sel)
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return 0;
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- desc = get_desc(sel);
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- if (!desc)
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+ if (!get_desc(&desc, sel))
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return 0;
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/*
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@@ -716,8 +718,8 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
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* not tested when checking the segment limits. In practice,
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* this means that the segment ends in (limit << 12) + 0xfff.
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*/
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- limit = get_desc_limit(desc);
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- if (desc->g)
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+ limit = get_desc_limit(&desc);
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+ if (desc.g)
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limit = (limit << 12) + 0xfff;
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return limit;
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@@ -741,7 +743,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
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*/
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int insn_get_code_seg_params(struct pt_regs *regs)
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{
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- struct desc_struct *desc;
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+ struct desc_struct desc;
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short sel;
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if (v8086_mode(regs))
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@@ -752,8 +754,7 @@ int insn_get_code_seg_params(struct pt_regs *regs)
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if (sel < 0)
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return sel;
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- desc = get_desc(sel);
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- if (!desc)
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+ if (!get_desc(&desc, sel))
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return -EINVAL;
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/*
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@@ -761,10 +762,10 @@ int insn_get_code_seg_params(struct pt_regs *regs)
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* determines whether a segment contains data or code. If this is a data
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* segment, return error.
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*/
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- if (!(desc->type & BIT(3)))
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+ if (!(desc.type & BIT(3)))
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return -EINVAL;
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- switch ((desc->l << 1) | desc->d) {
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+ switch ((desc.l << 1) | desc.d) {
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case 0: /*
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* Legacy mode. CS.L=0, CS.D=0. Address and operand size are
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* both 16-bit.
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--
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cgit 1.2-0.3.lf.el7
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