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Message-Id: <20200228000105.165012-11-thgarnie@chromium.org>
Date: Thu, 27 Feb 2020 16:00:55 -0800
From: Thomas Garnier <thgarnie@...omium.org>
To: kernel-hardening@...ts.openwall.com
Cc: kristen@...ux.intel.com,
keescook@...omium.org,
Thomas Garnier <thgarnie@...omium.org>,
Juergen Gross <jgross@...e.com>,
Thomas Hellstrom <thellstrom@...are.com>,
"VMware, Inc." <pv-drivers@...are.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
x86@...nel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v11 10/11] x86/paravirt: Adapt assembly for PIE support
If PIE is enabled, switch the paravirt assembly constraints to be
compatible. The %c/i constrains generate smaller code so is kept by
default.
Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
Acked-by: Juergen Gross <jgross@...e.com>
---
arch/x86/include/asm/paravirt_types.h | 32 +++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 84812964d3dd..82f7ca22e0ae 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -336,9 +336,32 @@ extern struct paravirt_patch_template pv_ops;
#define PARAVIRT_PATCH(x) \
(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
+#ifdef CONFIG_X86_PIE
+#define paravirt_opptr_call "a"
+#define paravirt_opptr_type "p"
+
+/*
+ * Alternative patching requires a maximum of 7 bytes but the relative call is
+ * only 6 bytes. If PIE is enabled, add an additional nop to the call
+ * instruction to ensure patching is possible.
+ *
+ * Without PIE, the call is reg/mem64:
+ * ff 14 25 68 37 02 82 callq *0xffffffff82023768
+ *
+ * With PIE, it is relative to %rip and take 1-less byte:
+ * ff 15 fa d9 ff 00 callq *0xffd9fa(%rip) # <pv_ops+0x30>
+ *
+ */
+#define PARAVIRT_CALL_POST "nop;"
+#else
+#define paravirt_opptr_call "c"
+#define paravirt_opptr_type "i"
+#define PARAVIRT_CALL_POST ""
+#endif
+
#define paravirt_type(op) \
[paravirt_typenum] "i" (PARAVIRT_PATCH(op)), \
- [paravirt_opptr] "i" (&(pv_ops.op))
+ [paravirt_opptr] paravirt_opptr_type (&(pv_ops.op))
#define paravirt_clobber(clobber) \
[paravirt_clobber] "i" (clobber)
@@ -377,9 +400,10 @@ int paravirt_disable_iospace(void);
* offset into the paravirt_patch_template structure, and can therefore be
* freely converted back into a structure offset.
*/
-#define PARAVIRT_CALL \
- ANNOTATE_RETPOLINE_SAFE \
- "call *%c[paravirt_opptr];"
+#define PARAVIRT_CALL \
+ ANNOTATE_RETPOLINE_SAFE \
+ "call *%" paravirt_opptr_call "[paravirt_opptr];" \
+ PARAVIRT_CALL_POST
/*
* These macros are intended to wrap calls through one of the paravirt
--
2.25.1.481.gfbce0eb801-goog
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