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| author | Tobin C. Harding <me@tobin.cc> | 2017-12-19 22:17:17 +0100 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2017-12-21 21:39:27 +0100 |
| commit | 227d1a61ed87033285d187214f305c27895176f9 (patch) | |
| tree | 023f89073768511726dafaebb54dbeb28944dfde /Documentation/security/self-protection.rst | |
| parent | doc: update kptr_restrict documentation (diff) | |
| download | linux-227d1a61ed87033285d187214f305c27895176f9.tar.xz linux-227d1a61ed87033285d187214f305c27895176f9.zip | |
doc: add documentation on printing kernel addresses
Hashing addresses printed with printk specifier %p was implemented
recently. During development a number of issues were raised regarding
leaking kernel addresses to userspace. Other documentation was updated but
security/self-protection missed out.
Add self-protection documentation regarding printing kernel addresses.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/security/self-protection.rst')
| -rw-r--r-- | Documentation/security/self-protection.rst | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/security/self-protection.rst b/Documentation/security/self-protection.rst index 60c8bd8b77bf..0f53826c78b9 100644 --- a/Documentation/security/self-protection.rst +++ b/Documentation/security/self-protection.rst @@ -270,6 +270,21 @@ attacks, it is important to defend against exposure of both kernel memory addresses and kernel memory contents (since they may contain kernel addresses or other sensitive things like canary values). +Kernel addresses +---------------- + +Printing kernel addresses to userspace leaks sensitive information about +the kernel memory layout. Care should be exercised when using any printk +specifier that prints the raw address, currently %px, %p[ad], (and %p[sSb] +in certain circumstances [*]). Any file written to using one of these +specifiers should be readable only by privileged processes. + +Kernels 4.14 and older printed the raw address using %p. As of 4.15-rc1 +addresses printed with the specifier %p are hashed before printing. + +[*] If KALLSYMS is enabled and symbol lookup fails, the raw address is +printed. If KALLSYMS is not enabled the raw address is printed. + Unique identifiers ------------------ |