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Subject[tip: x86/seves] x86/umip: Factor out instruction fetch
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: 172b75e56b08846e6fb07a88e5685ce4e24f4620
Gitweb: https://git.kernel.org/tip/172b75e56b08846e6fb07a88e5685ce4e24f4620
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:09 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 19:45:24 +02:00

x86/umip: Factor out instruction fetch

Factor out the code to fetch the instruction from user-space to a helper
function.

No functional changes.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-9-joro@8bytes.org
---
arch/x86/include/asm/insn-eval.h | 2 ++-
arch/x86/kernel/umip.c | 26 ++++-----------------
arch/x86/lib/insn-eval.c | 38 +++++++++++++++++++++++++++++++-
3 files changed, 46 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 2b6ccf2..b8b9ef1 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -19,5 +19,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
int insn_get_code_seg_params(struct pt_regs *regs);
+int insn_fetch_from_user(struct pt_regs *regs,
+ unsigned char buf[MAX_INSN_SIZE]);

#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 2c304fd..ad135be 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -335,11 +335,11 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
*/
bool fixup_umip_exception(struct pt_regs *regs)
{
- int not_copied, nr_copied, reg_offset, dummy_data_size, umip_inst;
- unsigned long seg_base = 0, *reg_addr;
+ int nr_copied, reg_offset, dummy_data_size, umip_inst;
/* 10 bytes is the maximum size of the result of UMIP instructions */
unsigned char dummy_data[10] = { 0 };
unsigned char buf[MAX_INSN_SIZE];
+ unsigned long *reg_addr;
void __user *uaddr;
struct insn insn;
int seg_defs;
@@ -347,26 +347,12 @@ bool fixup_umip_exception(struct pt_regs *regs)
if (!regs)
return false;

- /*
- * If not in user-space long mode, a custom code segment could be in
- * use. This is true in protected mode (if the process defined a local
- * descriptor table), or virtual-8086 mode. In most of the cases
- * seg_base will be zero as in USER_CS.
- */
- if (!user_64bit_mode(regs))
- seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
-
- if (seg_base == -1L)
- return false;
-
- not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
- sizeof(buf));
- nr_copied = sizeof(buf) - not_copied;
+ nr_copied = insn_fetch_from_user(regs, buf);

/*
- * The copy_from_user above could have failed if user code is protected
- * by a memory protection key. Give up on emulation in such a case.
- * Should we issue a page fault?
+ * The insn_fetch_from_user above could have failed if user code
+ * is protected by a memory protection key. Give up on emulation
+ * in such a case. Should we issue a page fault?
*/
if (!nr_copied)
return false;
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 5e69603..947b7f1 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1367,3 +1367,41 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
return (void __user *)-1L;
}
}
+
+/**
+ * insn_fetch_from_user() - Copy instruction bytes from user-space memory
+ * @regs: Structure with register values as seen when entering kernel mode
+ * @buf: Array to store the fetched instruction
+ *
+ * Gets the linear address of the instruction and copies the instruction bytes
+ * to the buf.
+ *
+ * Returns:
+ *
+ * Number of instruction bytes copied.
+ *
+ * 0 if nothing was copied.
+ */
+int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
+{
+ unsigned long seg_base = 0;
+ int not_copied;
+
+ /*
+ * If not in user-space long mode, a custom code segment could be in
+ * use. This is true in protected mode (if the process defined a local
+ * descriptor table), or virtual-8086 mode. In most of the cases
+ * seg_base will be zero as in USER_CS.
+ */
+ if (!user_64bit_mode(regs)) {
+ seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
+ if (seg_base == -1L)
+ return 0;
+ }
+
+
+ not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
+ MAX_INSN_SIZE);
+
+ return MAX_INSN_SIZE - not_copied;
+}
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