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If someone has the silly idea to write something along those lines:
extern u64 foo(void);
void bar(struct arm_smccc_res *res)
{
arm_smccc_1_1_smc(0xbad, foo(), res);
}
they are in for a surprise, as this gets compiled as:
0000000000000588 <bar>:
588: a9be7bfd stp x29, x30, [sp, #-32]!
58c: 910003fd mov x29, sp
590: f9000bf3 str x19, [sp, #16]
594: aa0003f3 mov x19, x0
598: aa1e03e0 mov x0, x30
59c: 94000000 bl 0 <_mcount>
5a0: 94000000 bl 0 <foo>
5a4: aa0003e1 mov x1, x0
5a8: d4000003 smc #0x0
5ac: b4000073 cbz x19, 5b8 <bar+0x30>
5b0: a9000660 stp x0, x1, [x19]
5b4: a9010e62 stp x2, x3, [x19, #16]
5b8: f9400bf3 ldr x19, [sp, #16]
5bc: a8c27bfd ldp x29, x30, [sp], #32
5c0: d65f03c0 ret
5c4: d503201f nop
The call to foo "overwrites" the x0 register for the return value,
and we end up calling the wrong secure service.
A solution is to evaluate all the parameters before assigning
anything to specific registers, leading to the expected result:
0000000000000588 <bar>:
588: a9be7bfd stp x29, x30, [sp, #-32]!
58c: 910003fd mov x29, sp
590: f9000bf3 str x19, [sp, #16]
594: aa0003f3 mov x19, x0
598: aa1e03e0 mov x0, x30
59c: 94000000 bl 0 <_mcount>
5a0: 94000000 bl 0 <foo>
5a4: aa0003e1 mov x1, x0
5a8: d28175a0 mov x0, #0xbad
5ac: d4000003 smc #0x0
5b0: b4000073 cbz x19, 5bc <bar+0x34>
5b4: a9000660 stp x0, x1, [x19]
5b8: a9010e62 stp x2, x3, [x19, #16]
5bc: f9400bf3 ldr x19, [sp, #16]
5c0: a8c27bfd ldp x29, x30, [sp], #32
5c4: d65f03c0 ret
Reported-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.