Here it is not obvious why we load pt_regs->cx to %esi etc.
Lets improve comments.
Explain that here we combine two things: first, we reload registers
since some of them are clobbered by the C function we just called;
and we also convert 32-bit syscall params to 64-bit C ABI,
because we are going to jump back to syscall dispatch code.
Move reloading of 6th argument into the macro instead of having it
after each of two macro invocations.
No actual code changes here.
Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
CC: Linus Torvalds <torva...@linux-foundation.org>
CC: Steven Rostedt <rost...@goodmis.org>
CC: Ingo Molnar <mi...@kernel.org>
CC: Borislav Petkov <b...@alien8.de>
CC: "H. Peter Anvin" <h...@zytor.com>
CC: Andy Lutomirski <l...@amacapital.net>
CC: Oleg Nesterov <o...@redhat.com>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Alexei Starovoitov <a...@plumgrid.com>
CC: Will Drewry <w...@chromium.org>
CC: Kees Cook <keesc...@chromium.org>
CC: x...@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/entry/entry_64_compat.S | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 2c44180..0fa108c 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -185,12 +185,18 @@ sysexit_from_sys_call:
movl %ebx, %esi /* 2nd arg: 1st syscall arg */
movl %eax, %edi /* 1st arg: syscall number */
call __audit_syscall_entry
- movl ORIG_RAX(%rsp), %eax /* reload syscall number */
- movl %ebx, %edi /* reload 1st syscall arg */
- movl RCX(%rsp), %esi /* reload 2nd syscall arg */
- movl RDX(%rsp), %edx /* reload 3rd syscall arg */
- movl RSI(%rsp), %ecx /* reload 4th syscall arg */
- movl RDI(%rsp), %r8d /* reload 5th syscall arg */
+ /*
+ * We are going to jump back to syscall dispatch.
+ * Prepare syscall args as required by 64-bit C ABI.
+ * Clobbered registers are loaded from pt_regs on stack.
+ */
+ movl ORIG_RAX(%rsp), %eax /* syscall number */
+ movl %ebx, %edi /* arg1 */
+ movl RCX(%rsp), %esi /* arg2 */
+ movl RDX(%rsp), %edx /* arg3 */
+ movl RSI(%rsp), %ecx /* arg4 */
+ movl RDI(%rsp), %r8d /* arg5 */
+ movl %ebp, %r9d /* arg6 */
.endm
.macro auditsys_exit exit
@@ -221,7 +227,6 @@ sysexit_from_sys_call:
sysenter_auditsys:
auditsys_entry_common
- movl %ebp, %r9d /* reload 6th syscall arg */
jmp sysenter_dispatch
sysexit_audit:
@@ -379,7 +384,6 @@ sysretl_from_sys_call:
#ifdef CONFIG_AUDITSYSCALL
cstar_auditsys:
auditsys_entry_common
- movl %ebp, %r9d /* reload 6th syscall arg */
jmp cstar_dispatch
sysretl_audit:
--
1.8.1.4
--
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