gdb: Implement amd64 linux shadow stack support for inferior calls.

This patch enables inferior calls to support Intel's Control-Flow
Enforcement Technology (CET), which provides the shadow stack feature
for the x86 architecture.
Following the restriction of the linux kernel, enable inferior calls
for amd64 only.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Luis Machado <luis.machado@arm.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4c3b7f2..a01406f 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -27037,6 +27037,38 @@ registers
 
 @end itemize
 
+@subsubsection Intel Control-Flow Enforcement Technology.
+@cindex Intel Control-Flow Enforcement Technology.
+
+The @dfn{Intel Control-Flow Enforcement Technology} (@acronym{Intel CET})
+provides two capabilities to defend against ``Return-oriented Programming''
+and ``call/jmp-oriented programming'' style control-flow attacks:
+
+@itemize @bullet
+@item Shadow Stack:
+A shadow stack is a second stack for a program.  It holds the return
+addresses pushed by the call instruction.  The @code{RET} instruction pops the
+return addresses from both call and shadow stack.  If the return addresses from
+the two stacks do not match, the processor signals a control protection
+exception.
+@item Indirect Branch Tracking (IBT):
+When IBT is enabled, the CPU implements a state machine that tracks
+indirect @code{JMP} and @code{CALL} instructions.  The state machine can
+be either IDLE or WAIT_FOR_ENDBRANCH.  When a @code{JMP} or @code{CALL} is
+executed the state machine chages to the WAIT_FOR_ENDBRANCH state.  In
+WAIT_FOR_ENDBRANCH state the next instruction in the program stream
+must be an @code{ENDBR} instruction, otherwise the processor signals a
+control protection exception.  After executing a @code{ENDBR} instruction
+the state machine returns to the IDLE state.
+@end itemize
+
+Impact on Call/Print:
+Inferior calls in @value{GDBN} reset the current PC to the beginning of the
+function that is called.  No call instruction is executed, but the @code{RET}
+instruction actually is.  To avoid a control protection exception due to the
+missing return address on the shadow stack, @value{GDBN} pushes the new return
+address to the shadow stack and updates the shadow stack pointer.
+
 @node Alpha
 @subsection Alpha