From: Michael Ellerman Date: Tue, 24 Jun 2008 01:32:24 +0000 (+1000) Subject: powerpc: Make create_branch() return errors if the branch target is too large X-Git-Tag: v2.6.27-rc1~1058^2~98 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=053a858efa46c9ab86363b271374ec02ad2af753;p=linux-2.6 powerpc: Make create_branch() return errors if the branch target is too large If you pass a target value to create_branch() which is more than 32MB - 4, or - 32MB away from the branch site, then it's impossible to create an immediate branch. The current code doesn't check, which will lead to us creating a branch to somewhere else - which is bad. For code that cares to check we return 0, which is easy to check for, and for code that doesn't at least we'll be creating an illegal instruction, rather than a branch to some random address. Signed-off-by: Michael Ellerman Acked-by: Kumar Gala Signed-off-by: Paul Mackerras --- diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index 638dde313c..430f4c15d7 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -26,12 +26,18 @@ unsigned int create_branch(const unsigned int *addr, unsigned long target, int flags) { unsigned int instruction; + long offset; + offset = target; if (! (flags & BRANCH_ABSOLUTE)) - target = target - (unsigned long)addr; + offset = offset - (unsigned long)addr; + + /* Check we can represent the target in the instruction format */ + if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3) + return 0; /* Mask out the flags and target, so they don't step on each other. */ - instruction = 0x48000000 | (flags & 0x3) | (target & 0x03FFFFFC); + instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC); return instruction; }